question_answer

Three bells ring simultaneously at 11 am. They ring at regular intervals of 20 min, 30 min, 40 min, respectively. The time when all the three ring together next is                                                    [SSC (CGL) 2011]

A) 2 pm                

B) 1 pm 

C) 1 : 15 pm                     

D) 1 : 30 pm

Correct Answer: B

Solution :

Required time = LCM of 20, 30 and 40

\[\text{LCM}=10\times 2\times 3\times 2=120\]

Hence, the bells will simultaneously ring after 2 h, i.e. at 1 pm.