Question

1. At two crossroads signals, lights change after every 25 seconds and
45 seconds respectively. If they changed together at 9:20 am, then when
will they change together next?
(A) at 9:23:45 am (B) at 9:23:15 am
(C) at 9:23:30 am (D) at 9:23:00 am​

Answer 1

Answer:

(A) at 9:23:45 am

Step-by-step explanation:

The lights will change together at 9:23:45 am

1) Both the lights will change together at a common multiple.

2) So, we can find the Least Common Multiple of both the lights i.e 25 and 45

3) 25=5×5 and 45= 5×9

The LCM would be 5×5×9 = 225

4) Hence both lights will change after 225 seconds i.e 3 min 45 seconds