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Answer :

Temperature at 12 noon was 10°C above zero i.e. +10°C

Rate of decrease in temperature per hour = 2°C

Number of hours from 12 noon to midnight = 12

Therefore Change in temperature in 12 hours
= 12 × (-2°C) = -24°C
Therefore Temperature at midnight
= +10°C + (-24°C) = -14°C
Hence, the required temperature at midnight =-14°C
Difference in temperature between + 10°C and -8°C
= +10°C – (-8°C) = +10°C + 8°C = 18°C
Number of hours required = 18?C ÷ 2?C= 9 hours
Therefore Time after 9 hours from 12 noon = 9 pm.

- Q.1 Evaluate each of the following: (a) (-30) ÷ 10 (b) 50 ÷ (-5) (c) (-36) ÷ (-9) (d) (-49) ÷ (49) (e) 13 ÷ [(-2) + 1] (f) 0 ÷ (-12) (g) (-31) ÷ [(-30) + (-1)] (h) [(-36) ÷ 12] ÷ 3 (i) [(-6) + 5] ÷ [(-2) + 1]
- Q.2 Verify that a ÷ (b + c) \(\neq \)(a ÷ b) + (a ÷ c) for each of the following values of a, b and c. (?) a = 12, b = – 4, c = 2 (b) a = (-10), b = 1, c = 1
- Q.3 Fill in the blanks: (a) 369 ÷ ___ = 369 (b) (-75) ÷ ___ = -1 (c) (-206) ÷ ___ =1 (d) -87 ÷ ___ = -87 (e) ___ ÷ 1 = -87 (f) _____ ÷ 48 = –1<br (g) 20 ÷ ___ = -2
- Q.4 Write five pairs of integers (a, b) such that a ÷ b = -3. One such pair is (6, -2) because 6 + (-2) = -3.
- Q.6 In a class test (+3) marks are given for every correct answer and (-2) marks are given for every incorrect answer and no marks for not attempting any question: (i) Radhika scored 20 marks. If she has got 12 correct answers, how many questions has she attempted incorrectly? (ii) Mohini scores -5 marks in this test, though she has got 7 correct answers. How many questions has she attempted incorrectly?
- Q.7 An elevator descends into a nine shaft at the rate of 6 m/min. If the descent starts from 10 m above the ground level, how long will it take to reach -350 m.

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