Question

If 3 bells toll at every 10, 30 and 75 seconds. Find after how many seconds will they toll togeather.

• A. 150 seconds
• B. 5 seconds
• C. 75 seconds
• D. 15 seconds

Answer 1

The correct option is A 150 seconds

Given, 3 bells toll at every 10, 30 and 75 second.

To find after how many seconds they will toll togeather, we have to find LCM of 10, 30 and 75.

$\underset{–}{\text{LCM of 10, 30 and 75:}}$

$\begin{array}{cc}2& 10,30,75\\ 5& 5,15,75\\ 3& 1,3,15\\ 5& 1,1,5\\ & 1,1,1\end{array}$

$\therefore$ LCM of 10, 30 and 75 is:
$=2\times 5\times 3\times 5=150$

Hence, 3 bells toll togeather after every 150 seconds.