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10.Find the smallest number that is divisible by each of the numbers 8, 15 and 20.
Answer :

The smallest number divisible by 8, 15 and 20 is equal to their LCM.
\(\qquad \begin{array}{c|lcr} 2 & 8 \;,\;15\;,\;20\\ \hline 2 & 4 \;,\;15\;,\;10\\ \hline 2 & 2 \;,\;15\;,\;5\\ \hline 3 & 1 \;,\;15\;,\;5\\ \hline 5 & 1 \;,\;5\;,\;5\\ \hline & 1\;,\;1\;,\;1\\ \end{array} \)

LCM =\( 2 \times 2 \times 2 \times 3 \times 5 = 120\)

Here, 2, 3 and 5 have no pair.So they are multiplied to get the least number divisible by 8,15 and 20.

The required smallest square number =\( 120 \times 2 \times 3 \times 5 = 120 \times 30 = 3600\)