question_answer

Three electronic devices make a beep after every 48 s, 72 s and 108 s, respectively. They beeped together at 10 a.m. The time when they will next make a beep together at the earliest is [SSC CGL Tier II, 2017]

A) 10 : 07: 12 h

B) 10 : 07 : 24 h

C) 10 : 07 : 36 h

D) 10 : 07 : 48 h

Correct Answer: A

Solution :

[a] First we have to find out the LCM of 48 s, 72 s and 108 s.             \[\therefore \] LCM of 48 s, 72 s and 108 s = \[=2\times 2\times 2\times 2\times 3\times 3\times 3\,s\] \[=432\,\,s=\frac{432}{60}\min =7\min 12\,\,s\] \[\therefore \] Time of beep together of devices \[=10:00+07:12=10:07:12\]