Question

Three bells start chiming at the same time and they chime at the interval of 56 seconds, 72 seconds and 120 seconds respectively. After how many seconds will they chime again together?

• A. 1200 seconds
• B. 1120 seconds
• C. 2520 seconds
• D. 4320 seconds

Answer 1

The correct option is C 2520 seconds

The LCM of 56, 72, 120 will give us the time at which they chime again together.

$\begin{array}{cc}2& 56,72,120\\ 2& 28,36,60\\ 2& 14,18,30\\ 3& 7,9,15\\ 3& 7,3,5\\ 7& 7,1,5\\ 5& 1,1,5\\ & 1,1,1\end{array}$
LCM (56, 72, 120) = $2\times 2\times 2\times 3\times 3\times 7\times 5$ = 2520 seconds

Hence, the bells will chime together at 2520 seconds.