# NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

Written by Team Trustudies
Updated at 2021-05-07

## NCERT solutions for class 9 Maths Chapter 1 Number Systems Exercise 1.1

Q1 ) Is zero a rational number?Can you write it in the form $$\frac{p}{q}$$,where p and q are integers and $$q \ne 0$$.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

Yes, we may rewrite 0 as $$\frac{0}{1} , \frac{0}{2} , \frac{0}{3}$$

(where 0 and 1,2,3 are integers and q=1,2,3 which is not equal to zero).

Because we know that a number is called as rational number if it can be expressed in $$\frac{p}{q}$$ form.

Q2 ) Find six rational numbers between 3 and 4.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

There can be infinitely many rational numbers between 3 and 4, one way to take them is

3=$$\frac{21}{(6+1)}$$, 4=$$\frac{28}{(6+1)}$$ .

The rational numbers between 3 and 4 therefore, will become
$$\frac{22}{7} ,\frac{23}{7} ,\frac{24}{7} ,\frac{25}{7} ,\frac{26}{7} ,\frac{27}{7}.$$

Another way to find middle rational number between two number
$$\Rightarrow$$ $$\frac{\frac{21}{7} + \frac{28}{7} }{2}$$
= $$\frac{\frac{49}{7} }{2}$$
= $$\frac{7}{2}$$.

As,$$\frac{ 21}{7} < \frac{7}{2} < \frac{28}{7}$$.

Rational no. between$$\frac{21}{7}$$ and $$\frac{7}{2}$$ will become

$$\Rightarrow$$ $$\frac{\frac{21}{7} + \frac{7}{2} }{2}$$
= $$\frac{\frac{91}{14} }{2}$$
= $$\frac{91}{28}$$ .

As,$$\frac{21}{7} < \frac{91}{28} < \frac{7}{2} < \frac{28}{7}$$.

Similarly, the other group of rational numbers between 3 and 4 will become

$$\frac{175}{56} , \frac{91}{28} , \frac{7}{2} , \frac{203}{56} , \frac{105}{28} , \frac{217}{56}$$ .

Q3 ) Find five rational numbers between $$\frac{3}{5}$$ and $$\frac{4}{5}$$.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

There can be infinitely many rational numbers between $$\frac{3}{5}$$ and $$\frac{4}{5}$$ , one way to take them is

$$\frac{3}{5} = \frac{3×10}{5×10} = \frac{30}{50}$$
$$\frac{4}{5} = \frac{4×10}{5×10} = \frac{40}{50}$$

Therefore the rational number between $$\frac{30}{50}$$ and $$\frac{40}{50}$$ are

$$\frac{31}{50} ,\frac{32}{50} \frac{33}{50} ,\frac{34}{50} , \frac{35}{50}$$

Another way to find middle rational number between two number $$\frac{3}{5}$$ and $$\frac{4}{5}$$is

$$\Rightarrow$$ $$\frac{\frac{3}{5} + \frac{4}{5} }{2}$$
= $$\frac{\frac{7}{5} }{2}$$
= $$\frac{7}{10}$$ .

As, $$\frac{3}{5} < \frac{7}{10} < \frac{4}{5}$$ .

Now,a rational number between $$\frac{3}{5}$$ and $$\frac{7}{10}$$ is

$$\Rightarrow$$$$\frac{\frac{3}{5} + \frac{7}{10} }{2}$$
=$$\frac{\frac{13}{10} }{2}$$
= $$\frac{13}{20}$$.

As, $$\frac{3}{5} < \frac{13}{20} < \frac{7}{10} < \frac{4}{5}$$.

Similarly, $$\frac{25}{40} , \frac{27}{40} , \frac{15}{20}$$ are rational numbers between $$\frac{3}{5}$$ and $$\frac{4}{5}$$.

Therefore, five rationals between numbers$$\frac{3}{5}$$ and $$\frac{4}{5}$$are

$$\frac{25}{40} , \frac{13}{20} , \frac{27}{40} , \frac{7}{10} , \frac{15}{20}$$.

Q4 ) State whether the following statements are true or false.Give reasons for your answers.
i)Every natural number is a whole number.
ii) Every integer is a whole number.
iii) Every rational number is a whole number.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i)True, because natural numbers are 1, 2, 3, 4,.............. and whole numbers are 0, 1, 2, 3, 4, 5,....... i.e. the collections of whole numbers contain all the natural numbers.

ii)False, because negative integers are not whole numbers.

iii)False, because for e.g. $$\frac{16}{23}$$ or $$\frac{7}{2}$$ are rational numbers who are not whole numbers.

## NCERT solutions for class 9 Maths Chapter 1 Number Systems Exercise 1.2

Q1 ) State whether the following statements are true or false. Justify your answers.
i) Every irrational number is a real number.
ii) Every point on the number line is of the form $$\sqrt{m}$$ , where m is a natural number.
iii)Every real number is an irrational number.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i) True, since (Real number = Rational number + Irrational number).

ii)False, because no negative number can be the square root of any natural number.

iii)False, as every irrational number is a real number but opposite is not true.

Q2 ) Are the square roots of all positive integers irrational? If not, give an example of the square root of a number that is a rational number.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

No, the square roots of all positive integers are not irrational.

For Example, $$\sqrt{9}$$ = 3 Here, '3' is a rational number.

While some numbers have irrational square roots, too.

Q3 ) Show how $$\sqrt{5}$$ can be represented on the number line.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

We know that, $$\sqrt{5}$$ = $$\sqrt{4 + 1}$$ = $$\sqrt{2^2 + 1^2}$$.

Draw a right angled triangle, OQP, such that OQ = 2 Units and PQ = 1 Unit And $$\angle{OQP} = 90°$$

Now, by using Pythagoras theorem, we have $$OQ^2 = OP^2 + PQ^2 = 2^2 + 1^2$$.

Therefore, OP = $$\sqrt{5}$$.
Now, take O as centre OP = $$\sqrt{5}$$ as radius, draw an arc, which intersects the line at point R.
Hence, the point R represents $$\sqrt{5}$$ .

Q4 ) Classroom activity (constructing the 'square root spiral').

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

Take a large sheet of paper and construct the ‘square root spiral’ in the following fashion.

Start with a point O and draw a line segment $$OP_1$$ of unit length. Draw a line segment $$P_1P_2$$ perpendicular to $$OP_1$$ of unit length.

Now, draw a line segment $$P_2P_3$$ perpendicular to $$OP_2$$ . Then draw a line segment $$P_3P_4$$ perpendicular to $$OP_3$$.

Continuing in this manner, you can get the line segment $$P_(n-1)Pn$$ by drawing a line segment of unit length perpendicular to $$OP_(n-1)$$ .

In This manner, you will have created the points $$P_2$$, $$P_3$$, $$P_4$$, $$P_5$$,........ and joined them to create a beautiful spiral depicting $$\sqrt{2}$$, $$\sqrt{3}$$, $$\sqrt{4}$$,......

## NCERT solutions for class 9 Maths Chapter 1 Number Systems Exercise 1.3

Q1 ) Write the following in decimal form and say what kind of decimal expansion each has:
i) $$\frac{36}{100}$$
ii) $$\frac{1}{11}$$
iii) $$4\frac{1}{8}$$
iv)$$\frac{3}{13}$$
v)$$\frac{2}{11}$$
vi)$$\frac{329}{400}$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i) Clearly, $$\frac{36}{100}$$ can be written as 0.36.
Therefore, it is a terminating decimal.

ii) Dividing 1 by 11, we get$$\require{enclose} \begin{array}{rll} 0.0909 && \hbox{(Explanations)} \\[-3pt] 11 \enclose{longdiv}{100}\kern-.2ex \\[-3pt] \underline{99\phantom{00}} && \hbox{(9 \times 11 = 99)} \\[-3pt] \phantom{0}100 && \hbox{(100 - 99 = 1)} \\[-3pt] \underline{\phantom{0}99} && \hbox{(9 \times 11 = 99)} \\[-3pt] \phantom{00}1 \end{array}$$Hence, $$\frac{1}{11}$$ can be written as 0.090909...
Therefore, it is a non-terminating decimal.

iii) We have, $$4\frac{1}{8}$$ = $$\frac{4×8+1}{8}$$ = $$\frac{33}{8}$$
Dividing 33 by 8, we get, $$\require{enclose} \begin{array}{rll} 4.125 && \hbox{(Explanations)} \\[-3pt] 8 \enclose{longdiv}{33}\kern-.2ex \\[-3pt] \underline{32\phantom{00}} && \hbox{(8 \times 4 = 32)} \\[-3pt] \phantom{0}10 && \hbox{(33 - 32 = 1)} \\[-3pt] \underline{8\phantom{00}} && \hbox{(8 \times 1 = 8)} \\[-3pt] \phantom{0}20 && \hbox{(10 - 8 = 2)} \\[-3pt] \underline{16\phantom{00}} && \hbox{(8 \times 2 = 16)} \\[-3pt] \phantom{0}40 && \hbox{(20 - 16 = 4)} \\[-3pt] \underline{\phantom{0}40} && \hbox{(8 \times 5 = 40)} \\[-3pt] \phantom{00}0 \end{array}$$Hence, $$4\frac{1}{8}$$ can be written as 4.125
Therefore, it is a terminating decimal.

iv) We have, $$\frac{3}{13}$$
Dividing 3 by 13, we get, $$\require{enclose} \begin{array}{rll} 0.230769 && \hbox{(Explanations)} \\[-3pt] 13 \enclose{longdiv}{30}\kern-.2ex \\[-3pt] \underline{26\phantom{00}} && \hbox{(2 \times 13 = 26)} \\[-3pt] \phantom{0}40 && \hbox{(30 - 26 = 4)} \\[-3pt] \underline{39\phantom{00}} && \hbox{(3 \times 13 = 39)} \\[-3pt] \phantom{0}100 && \hbox{(40 - 39 = 1)} \\[-3pt] \underline{91\phantom{00}} && \hbox{(7 \times 13 = 91)} \\[-3pt] \phantom{0}90 && \hbox{(100 - 91 = 4)} \\[-3pt] \underline{78\phantom{00}} && \hbox{(6 \times 13 = 78)} \\[-3pt] \phantom{0}120 && \hbox{(90 - 78 = 12)} \\[-3pt] \underline{\phantom{0}117} && \hbox{(9 \times 13 = 117)} \\[-3pt] \phantom{00}3 \end{array}$$Hence, $$\frac{3}{13}$$ can be written as 0.230769
Therefore, it is a non-terminating decimal.

v) We have, $$\frac{2}{11}$$
Dividing 2 by 11, we get, $$\require{enclose} \begin{array}{rll} 0.1818 && \hbox{(Explanations)} \\[-3pt] 11 \enclose{longdiv}{20}\kern-.2ex \\[-3pt] \underline{11\phantom{00}} && \hbox{(1 \times 11 = 11)} \\[-3pt] \phantom{0}90 && \hbox{(20 - 11 = 9)} \\[-3pt] \underline{88\phantom{00}} && \hbox{(8 \times 11 = 11)} \\[-3pt] \phantom{0}20 && \hbox{(90 - 88 = 2)} \\[-3pt] \underline{11\phantom{00}} && \hbox{(1 \times 11 = 11)} \\[-3pt] \phantom{0}90 && \hbox{(20 - 11 = 9)} \\[-3pt] \underline{\phantom{0}88} && \hbox{(8 \times 11 = 88)} \\[-3pt] \phantom{00}2 \end{array}$$Hence, $$\frac{2}{11}$$ can be written as 0.181818...
Therefore, it is a non-terminating decimal.

vi) We have, $$\frac{329}{400}$$
Dividing 329 by 400, we get, $$\require{enclose} \begin{array}{rll} 0.8225 && \hbox{(Explanations)} \\[-3pt] 400 \enclose{longdiv}{3290}\kern-.2ex \\[-3pt] \underline{3200\phantom{00}} && \hbox{(8 \times 400 = 3200)} \\[-3pt] \phantom{0}900 && \hbox{(3290 - 3200 = 9)} \\[-3pt] \underline{800\phantom{00}} && \hbox{(2 \times 400 = 800)} \\[-3pt] \phantom{0}1000 && \hbox{(900 - 800 = 100)} \\[-3pt] \underline{800\phantom{00}} && \hbox{(2 \times 400 = 800)} \\[-3pt] \phantom{0}2000 && \hbox{(1000 - 800 = 200)} \\[-3pt] \underline{\phantom{0}2000} && \hbox{(5 \times 400 = 400)} \\[-3pt] \phantom{00}0 \end{array}$$Hence, $$\frac{329}{400}$$ can be written as 0.8225
Therefore, it is a terminating decimal.

Q2 ) You know that $$\frac{1}{7} = 0\overline{.142857.}$$ Can you predict what the decimal expansions of $$\frac{2}{7} , \frac{3}{7} , \frac{4}{7} , \frac{5}{7} , \frac{6}{7}$$ are, without actually doing the long division. If so, how?
[Hint Study the remainders while finding the value $$\frac{1}{7}$$ of carefully.]

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

We have,
$$\frac{1}{7} = 0\overline{.142857}$$

So we can say that,
$$\because \frac{2}{7} = 2 × \frac{1}{7}$$
$$\Rightarrow \frac{2}{7} = 2 × 0\overline{.142857}$$
$$\Rightarrow \frac{2}{7} = 0\overline{.285714}$$

$$\because \frac{3}{7} = 3 × \frac{1}{7}$$
$$\Rightarrow \frac{3}{7} = 3 × 0\overline{.142857}$$
$$\Rightarrow \frac{3}{7} = 0\overline{.428571}$$

$$\because \frac{4}{7} = 4 × \frac{1}{7}$$
$$\Rightarrow \frac{4}{7} = 4 × 0\overline{.142857}$$
$$\Rightarrow \frac{4}{7} = 0\overline{.571428}$$

$$\because \frac{5}{7} = 5 × \frac{1}{7}$$
$$\Rightarrow \frac{5}{7} = 5 × 0\overline{.142857}$$
$$\Rightarrow \frac{5}{7} = 0\overline{.714285}$$

$$\because \frac{6}{7} = 6 × \frac{1}{7}$$
$$\Rightarrow \frac{6}{7} = 6 ×0 \overline{.142857}$$
$$\Rightarrow \frac{6}{7} = 0\overline{.857142}$$

Q3 ) Express the following in the form $$\frac{p}{q}$$ where p and q are integers and $$q \ne 0$$ .
i)$$0\overline{.6}$$
ii)$$0.4\overline{7}$$
iii)$$0\overline{.001}$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i) Let x = 0.66666... .......(i)

multiplying by eq. (i) by 10 , we get,

10 x = 6.666...... .....(ii)

On subtracting Eq. (ii) from Eq. (i), we get ,

(10 x – x) = (6.666…) – (0.666…)
$$\Rightarrow$$ 9x = 6
$$\Rightarrow$$x = $$\frac{6}{9}$$
Hence, x = $$\frac{2}{3}$$

ii)Let x = 0.477777... .......(i)

multiplying by eq. (i) by 10 , we get,

10 x = 4.777....... ......(ii)

On subtracting Eq. (ii) from Eq. (i), we get,

(10 x – x) = (4.777) - (0.4777)
$$\Rightarrow$$ 9x = 4.3
$$\Rightarrow$$ x = $$\frac{4.3}{9}$$
Hence, x = $$\frac{43}{90}$$

iii)Let x = 0.001001001...... ...... (i)

multiplying by eq. (i) by 1000 , we get,

1000 x = 1.001001001.... .....(ii)

On subtracting Eq. (ii) from Eq. (i), we get

(1000 x – x) = (1.001001001....) – (0.001001001....)
$$\Rightarrow$$ 999x = 1
Hence, x = $$\frac{1}{999}$$

Q4 ) Express 0.99999… in the form $$\frac{p}{q}$$ . Are you surprised by your answer?

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

Let,
x = 0.9999.... (i)

multiplying by eq. (i) by 10 , we get,

10 x = 9.9999......(ii)

On subtracting Eq. (ii) from Eq. (i), we get

(10 x – x) = (9.99999…) – (0.99999…)
$$\Rightarrow$$ 9x = 9
$$\Rightarrow$$ x = 1

Yes I m surprised
0.9999999..... = 1 because it is extremely closed by 1

Q5 ) What can the maximum number of digits be in the repeating block of digits in the decimal expansion of $$\frac{1}{17}$$ ?

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

We know that, the maximum number of digits in the repeating block of digits in the decimal expansion of $$\frac{1}{17}$$ is 17 – 1 = 16. $$\require{enclose} \begin{array}{rll} 0.0588235294117647 && \hbox{(Explanations)} \\[-3pt] 17 \enclose{longdiv}{100}\kern-.2ex \\[-3pt] \underline{85\phantom{00}} && \hbox{(5 \times 17 = 85)} \\[-3pt] \phantom{0}150 && \hbox{(100 - 85 = 15)} \\[-3pt] \underline{136\phantom{00}} && \hbox{(8 \times 17 = 136)} \\[-3pt] \phantom{0}140 && \hbox{(150 - 136 = 14)} \\[-3pt] \underline{136\phantom{00}} && \hbox{(8 \times 17 = 136)} \\[-3pt] \phantom{0}40 && \hbox{(140 - 136 = 4)} \\[-3pt] \underline{34\phantom{00}} && \hbox{(2 \times 17 = 34)} \\[-3pt] \phantom{0}60 && \hbox{(40 - 34 = 6)} \\[-3pt] \underline{51\phantom{00}} && \hbox{(3 \times 17 = 51)} \\[-3pt] \phantom{0}90 && \hbox{(60 - 51 = 9)} \\[-3pt] \underline{85\phantom{00}} && \hbox{(5 \times 17 = 85)} \\[-3pt] \phantom{0}50 && \hbox{(90 - 85 = 5)} \\[-3pt] \underline{34\phantom{00}} && \hbox{(2 \times 17 = 34)} \\[-3pt] \phantom{0}160 && \hbox{(50 - 34 = 16)} \\[-3pt] \underline{153\phantom{00}} && \hbox{(9 \times 17 = 153)} \\[-3pt] \phantom{0}70 && \hbox{(160 - 153 = 7)} \\[-3pt] \underline{68\phantom{00}} && \hbox{(4 \times 17 = 68)} \\[-3pt] \phantom{0}20 && \hbox{(70 - 68 = 2)} \\[-3pt] \underline{17\phantom{00}} && \hbox{(1 \times 17 = 17)} \\[-3pt] \phantom{0}30 && \hbox{(20 - 17 = 3)} \\[-3pt] \underline{28\phantom{00}} && \hbox{(2 \times 17 = 28)} \\[-3pt] \phantom{0}130 && \hbox{(30 - 17 = 13)} \\[-3pt] \underline{119\phantom{00}} && \hbox{(7 \times 17 = 119)} \\[-3pt] \phantom{0}110 && \hbox{(130 - 119 = 11)} \\[-3pt] \underline{102\phantom{00}} && \hbox{(6 \times 17 = 136)} \\[-3pt] \phantom{0}80 && \hbox{(110 - 102 = 8)} \\[-3pt] \underline{68\phantom{00}} && \hbox{(4 \times 17 = 68)} \\[-3pt] \phantom{0}40 && \hbox{(80 - 68 = 120)} \\[-3pt] \underline{\phantom{0}119} && \hbox{(7 \times 400 = 119)} \\[-3pt] \phantom{00}1 \end{array}$$ We have, Thus, $$\frac{1}{17}$$= $$= 0\overline{.0588235294117647}$$
i.e.a block of 16 digits is repeated.

Q6 ) Look at several examples of rational numbers in the form $$\frac{p}{q}$$ ($$q \neq 0$$). Where, p and q are integers with no common factors other than 1 and having terminating decimal representations(expansions).
Can you guess what property q must satisfy?

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

Considering some rational numbers in the form $$\frac{p}{q}$$( $$q \neq 0$$ )with no common factors other than 1 and having terminating decimal representations(expansions).

we can say, the various such rational numbers are $$\frac{1}{2} , \frac{7}{125} , \frac{1}{4} , \frac{19}{20}$$, etc.

$$\frac{1}{2} = \frac{(1 × 5)}{(2 × 5)} = \frac{5}{10} = 0.5.$$

$$\frac{7}{125} =\frac{(7 × 8)}{(125 × 8)} = \frac{56}{1000} = 0.056$$

$$\frac{1}{4} = \frac{(1 × 25)}{(25 × 4)} = \frac{25}{100} = 0.25$$

$$\frac{19}{25} = \frac{(19 × 4)}{(25 × 4)} = \frac{76}{100} = 0.76$$

In all the cases mentioned above, we think of the natural number which when multiplied by their respective denominators gives 10 or a power of 10.

Thus, we find that, the decimal expansion of above numbers are terminating.

Along with, we see that the denominator of above numbers i.e. q is in the form has only powers of 2 or power of 5 or both of them.

Q7 ) Write three numbers whose decimal expansions are non-terminating non-recurring.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

The required numbers are as follows :

i) 4.020020002000002

ii)0.36366366636666

iii) 0.101100110001

Q8 ) Find three different irrational numbers between the rational numbers $$\frac{5}{7}$$and $$\frac{9}{11}$$.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

To find irrational numbers, firstly we shall divide 5 by 7 and 9 by 11,
So, for $$\frac{9}{11}$$,
we get, $$\require{enclose} \begin{array}{rll} 0.8181 && \hbox{(Explanations)} \\[-3pt] 11 \enclose{longdiv}{90}\kern-.2ex \\[-3pt] \underline{88\phantom{00}} && \hbox{(8 \times 11 = 88)} \\[-3pt] \phantom{0}20 && \hbox{(90 - 88 = 2)} \\[-3pt] \underline{11\phantom{00}} && \hbox{(1 \times 11 = 11)} \\[-3pt] \phantom{0}90 && \hbox{(20 - 11 = 9)} \\[-3pt] \underline{\phantom{0}88} && \hbox{(8 \times 11 = 88)} \\[-3pt] \phantom{00}2 \end{array}$$ Now, for $$\frac{5}{7}$$,
we get,$$\require{enclose} \begin{array}{rll} 0.714285 && \hbox{(Explanations)} \\[-3pt] 7 \enclose{longdiv}{50}\kern-.2ex \\[-3pt] \underline{49\phantom{00}} && \hbox{(7 \times 7 = 49)} \\[-3pt] \phantom{0}10 && \hbox{(50 - 49 = 1)} \\[-3pt] \underline{7\phantom{00}} && \hbox{(1 \times 7 = 7)} \\[-3pt] \phantom{0}30 && \hbox{(10 - 7 = 3)} \\[-3pt] \underline{28\phantom{00}} && \hbox{(4 \times 7 = 28)} \\[-3pt] \phantom{0}20 && \hbox{(30 - 28 = 2)} \\[-3pt] \underline{14\phantom{00}} && \hbox{(2 \times 7 = 14)} \\[-3pt] \phantom{0}60 && \hbox{(20 - 14 = 6)} \\[-3pt] \underline{56\phantom{00}} && \hbox{(8 \times 7 = 56)} \\[-3pt] \phantom{0}40 && \hbox{(60 - 56 = 4)} \\[-3pt] \underline{\phantom{0}35} && \hbox{(5 \times 7 = 35)} \\[-3pt] \phantom{00}5 \end{array}$$ Thus, $$\frac{5}{7} = 0\overline{.714285} = 0.71428571428...$$

$$\frac{9}{11} = 0\overline{.818181} = 0.8181818.....$$

Therefore, the three rational numbers between these will be

0.74074007400074000074...

0.7750775007750007750000...

0.80800800080000...

Q9 ) Classify the following numbers as rational or irrational :
i)$$\sqrt{23}$$
ii)$$\sqrt{225}$$
iii) 0.3796
iv) 7.478478.....
v)1.101001000100001.....

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i) Irrational (Since, it is not a perfect square).

ii)Rational (Since, it is a perfect square).

iii)0.3796 = Rational (terminating)

iv) 7.478478… = Rational (non-terminating repeating.)

v)1.101001000100001… = Irrational (non-terminating non-repeating.)

## NCERT solutions for class 9 Maths Chapter 1 Number Systems Exercise 1.4

Q1 ) Visualize $$3\overline{.765}$$ on the number line, using successive magnification.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

We know that, 3.765... lies between 3 and 4.

So, let us divide the part of the number line between and 3 and 4 into 10 equal parts, mark each point of division and look at the portion between 3.7 and 3.8 through a magnifying glass.

Now 3.765..... lies between 3.7 and 3.8 Figure (i). Now, we imagine to divide this again into ten equal parts. The first mark will represent 3.71, the next 3.72 and soon.

To see this clearly, we magnify this as shown in Figure (ii). Again 3.765.... lie between 3.76 and 3.77 Figure (ii).

So, let us focus on this portion of the number line Figure (iii) and imagine dividing it again into ten equal parts Figure (iii).

Here, we can visualize that 3.761 is the first mark and 3.765...... is the 5th mark in these subdivisions.

We call this process of visualization of representation of number on the number line through a magnifying glass as the process of successive magnification.

So, we get seen that it is possible by sufficient successive magnification of visualize the position (or representation) of a real number with a terminating decimal expansion on the number line.

Q2 ) Visualize $$4\overline{.26}$$ on the number line, upto 4 Decimal places.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

We know that, by process of successive magnification and successively decrease the length of the portion of the number line in which 4.26... is located.

Since 4.26... is located between 4 and 5 and is divided into 10 equal parts Figure (i). In further, we locate 4.26... between 4.2 and 4.3 Figure (ii).

To get more accurate visualization of the representation, we divide this portion into 10 equal parts and use a magnifying glass to visualize that 4.26.... lies between 4.26 and 4.27.

To visualize 4.26... more clearly we divide again between 4.26 and 4.27 into 10 equal parts and visualize the representation of 4.26... between 4.262 and 4.263

Figure (iii).

Now, for a much better visualization between 4.262 and 4.263 is again divided into 10 equal parts Figure (iv).

Notice that 4.26..... is located closer to 4.263 then to 4.262 at 4.2627.

## NCERT solutions for class 9 Maths Chapter 1 Number Systems Exercise 1.5

Q1 ) Classify the following numbers as rational or irrational :
i)$$2 - \sqrt{5}$$
ii)$$(3 + \sqrt{23}) - \sqrt{23}$$
iii)$$\frac{2\sqrt{7} }{ 7\sqrt{7}}$$
iv)$$\frac{1}{\sqrt{2}}$$
v)$$2\pi$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i) Irrational number (Since, 2 is a rational number and 5 is an irrational number).
Therefore, $$2 - \sqrt{5}$$ is an irrational number.

ii)$$(3 + \sqrt{23}) - \sqrt{23}= 3$$ i.e. rational number .

iii) $$\frac{2\sqrt{7} }{7\sqrt{7}} = \frac{2}{7}$$ i.e. rational number

iv) $$\frac{1}{ \sqrt{2}}$$ is an irrational number because, as numerator is a rational number but denominator is an irrational number.

v) $$2\pi$$ is a Irrational number , since 2 is a rational number and $$\pi$$ is an irrational number. And product of rational number and irrational number is also irrational number.

Q2 ) Simplify each of the following expressions:
i) $$(3 + \sqrt{3})(2 + \sqrt{2})$$
ii) $$(3 + \sqrt{3})(3 - \sqrt{3})$$
iii) $$(\sqrt{5} + \sqrt{2})(\sqrt{5} + \sqrt{2})$$
iv)$$(\sqrt{5} + \sqrt{2})(\sqrt{5} - \sqrt{2})$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i) $$(3 + \sqrt{3})(2 + \sqrt{2})$$
$$\therefore$$ $$(3 + \sqrt{3})(2 + \sqrt{2})$$ $$= 6 + 3\sqrt{2} + 2\sqrt{3} + 6$$

ii) $$(3 + \sqrt{3})(3 - \sqrt{3})$$)
$$= 3^2 - (\sqrt{3})^2$$
Because, We know that,
($$a + b)(a - b) = a^2 - b^2$$
$$\therefore (3 + \sqrt{3})(3 - \sqrt{3})$$
$$= 9 -3 = 6$$

iii)$$(\sqrt{5} + \sqrt{2})^2$$
$$= (\sqrt{5})^2 + 2 × \sqrt{5}\sqrt{2} + (\sqrt{2})^2$$
Because, We know that, $$(a + b)^2 = a^2 + 2 × a × b + b^2$$
$$= 5 + 2\sqrt{10} + 2$$
$$\therefore (\sqrt{5} + \sqrt{2})^2 = 7 + 2\sqrt{10}$$

iv) $$(\sqrt{5} + \sqrt{2})(\sqrt{5} - \sqrt{2})$$
$$= (\sqrt{5})^2 - (\sqrt{2})^2$$
Because, We know that, $$(a + b)(a - b) = a^2 - b^2$$
$$\therefore$$ $$(\sqrt{5} + \sqrt{2})(\sqrt{5} - \sqrt{2})$$
$$= 5 -2 = 3$$

Q3 ) Recall, $$\pi$$ is defined as the ratio of the circumference (say c) of a circle to its diameter (say d).
That is, $$\pi = \frac{c}{d}$$ . This seems to contradict the fact that $$\pi$$ is irrational.
How will you resolve this contradiction?

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

First of all, there is not any contradiction. $$\pi$$ defined here has an approximate value of $$\frac{22}{7}$$ i.e. by comparing with $$\frac{c}{d}$$ .

Also, any value measured on scale or physically is an approx value.

Q4 ) Represent $$\sqrt{9.3}$$ on the number line.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

Firstly we draw AB = $$\sqrt{9.3}$$ units. Now, from B, mark a distance of 1 unit.

Let this point be C. Let O be the mid-point of AC. Now, draw a semi-circle with centre O and radius OA.

Let us draw a line perpendicular to AC passing through point B and intersecting the semi-circle at point D.

$$\therefore$$ the distance BD = $$\sqrt{9.3}$$ units.

Draw an arc with centre B and radius BD which intersects the number line at point E, then the point E represents $$\sqrt{9.3}$$ .

Q5 ) Rationalize the denominator of the following :
i)$$\frac{1}{\sqrt{7}}$$
ii)$$\frac{1}{\sqrt{7} } - \sqrt{6}$$
iii)$$\frac{1}{\sqrt{5}} + \sqrt{2}$$
iv)$$\frac{1}{\sqrt{7}} - 2$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

To rationalize the denominator, we need to multiply the irrational denominator by it's conjugate.
i) $$\frac{1}{\sqrt{7}}$$ × $$\frac{\sqrt{7}}{\sqrt{7}}$$
= $$\frac{\sqrt{7}}{7}$$

ii) $$\frac{1}{(\sqrt{7} - \sqrt{6})} × \frac{(\sqrt{7} + \sqrt{6})}{(\sqrt{7} + \sqrt{6})}$$
$$= \frac{(\sqrt{7} + \sqrt{6})}{(7-6)}$$
$$= \sqrt{7} + \sqrt{6}$$

iii) $$\frac{1}{(\sqrt{5} + \sqrt{2})}$$ × $$\frac{(\sqrt{5} - \sqrt{2})}{(\sqrt{5} - \sqrt{2})}$$
$$= \frac{(\sqrt{5} - \sqrt{2})}{(5 - 2)}$$
$$= \frac{(\sqrt{5} - \sqrt{2})}{3}$$

iv) $$\frac{1}{(\sqrt{7} - 2)}$$ × $$\frac{(\sqrt{7} + 2)}{(\sqrt{7} + 2)}$$
$$= \frac{(\sqrt{7} + 2)}{(7 - 4)}$$
$$= \frac{\sqrt{7} + 2}{3}$$

## NCERT solutions for class 9 Maths Chapter 1 Number Systems Exersice 1.6

Q1 ) Find :
i)$$(64)^{\frac{1}{2}}$$
ii)$$(32)^{\frac{1}{5}}$$
iii)$$(125)^{\frac{1}{3}}$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i)$$(64)^{\frac{1}{2}}$$
$$= (8 × 8)^{\frac{1}{2}}$$
$$= 8^{\frac{1}{2} × 2} =8$$

ii) $$(32)^{\frac{1}{5}}$$
$$= (2 × 2 × 2 × 2 × 2)^{\frac{1}{5}}$$
$$= 2^{\frac{1}{5} × 5}$$ =$$2$$

iii) $$(125)^{\frac{1}{3}}$$
$$= (5 × 5 × 5)^{\frac{1}{3}}$$
$$= 5^{3 × \frac{1}{3}}$$ = $$5$$

Q2 ) Find :
i)$$(9)^{\frac{3}{2}}$$
ii)$$(32)^{\frac{2}{5}}$$
iii)$$(16)^{\frac{3}{4}}$$
iv)$$(125)^{\frac{-1}{3}}$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i)$$(9)^{\frac{3}{2}}$$
$$= (3 × 3)^{\frac{3}{2}}$$
$$= 3^{2 × \frac{3}{2}}$$
$$= 3^{3} = 27$$

ii) $$(32)^{\frac{2}{5}}$$
$$= (2 × 2 × 2 × 2 × 2)^{\frac{2}{5}}$$
$$= 2^{\frac{2}{5} × 5}$$
$$= 2^2 = 4$$

iii) $$(16)^{\frac{3}{4}}$$
$$= (2 × 2 × 2 × 2)^{\frac{3}{4}}$$
$$= 2^{4 × \frac{3}{4}}$$
$$=2^{3} = 8$$

iv) $$(125)^{\frac{-1}{3}}$$
$$= (5 × 5 × 5)^{\frac{-1}{3}}$$
$$= 5^{3 × (\frac{-1}{3})}$$
$$= 5^{-1} = \frac{1}{5}$$

Q3 ) Find :
i)$$2^{\frac{2}{3} } × 2^{\frac{1}{5} }$$
ii)$$(\frac{1}{3^{3}})^{7}$$
iii)$$\frac{11^{\frac{1}{2} }}{11^{\frac{1}{4} }}$$
iv)$$7^{\frac{1}{2} } × 8^{\frac{1}{2} }$$

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems

i)$$2^{\frac{2}{3} } × 2^{\frac{1}{5} }$$
$$= 2^{\frac{2}{3} + \frac{1}{5} }$$
$$= 2^{\frac{(10+3)}{15} }$$
$$= 2^{\frac{13}{15} }$$

ii) $$(\frac{1}{3^{3}})^{7}$$
$$= \frac{1}{3^{3 × 7}}$$
$$= \frac{1}{3^{21}}$$
$$= 3^{-21}$$

iii)$$\frac{11^{\frac{1}{2} }}{11^{\frac{1}{4} }}$$
$$= 11^{( \frac{1}{2} - \frac{1}{4} ) }$$
$$= 11^{\frac{1}{4} }$$

iv)$$7^{\frac{1}{2} } × 8^{\frac{1}{2} }$$
$$= (7 × 8)^{\frac{1}{2} }$$
$$= 56^{\frac{1}{2} }$$

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