10th Class Mathematics Real Numbers Question Bank MCQs - Real Numbers

On Delhi road, three consecutive traffic lights change after 36,42 and 72 seconds. If the lights are first switched on at 9.00 am, at what time will they change simultaneously?

A) \[\text{9}:0\text{8}:0\text{4}\]

B) \[\text{9}:0\text{8}:\text{24}\]

C) \[\text{9}:0\text{8}:\text{44}\]

D) None of these

Correct Answer: B

Solution :

Sol. [b] LCM of \[\text{36,42}\] and \[\text{72 }=\text{5}0\text{4}\]

\[\text{5}0\text{4 sec}=\text{8 min 24 sec}\]

Hence, at \[\text{9}:0\text{8}:\text{24}\] they will change simultaneously.