Question

Three cannons fire shots at intervals of 12 seconds, 18 seconds and 60 seconds respectively. If they start firing at the same time, then after how many seconds will they fire together again?

• A. 3 minutes
• B. 4 minutes
• C. 5 minutes
• D. 6 minutes

Answer 1

The correct option is A

3 minutes

$\begin{array}{cc}2& 12,18,60\\ 2& 6,9,30\\ 3& 3,9,15\\ 3& 1,3,5\\ 5& 1,1,5\\ & 1,1,1\end{array}$
Time after which the cannons fire together = L.C.M of 12, 18, 60 $=2\times 2\times 3\times 3\times 5=180\text{seconds}=3\text{minutes}$