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
(B) at 9:23:15 am
(D) at 9:23:00 am
A
will they change together next?
(A) at 9:23:45 am
(C) at 9:23:30 am​

Answer 1

Correct Question :

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

Solution :

Here, it is mentioned that in two separate crossroad signals change at an interval of every 25 seconds and 45 seconds respectively .

So, let us find how long they take to change together .

The first interval is of 25 seconds and the other is of 45 seconds .

Time needed for them to change together : LCM of 25 and 45

> [ 25, 45]

> 5 [ 5, 9 ]

> 45 × 5

> 225 seconds.

> 180 seconds + 45 seconds.

> 3 mins 45 seconds .

They first changed at 9:20 am .

So, they will change together next at 9:23:45 am .

Thus , option A is the correct option .

________________________

Answer 2

Answer:

Correct Question :-

• At two crossroads signal, light change after every 25 seconds and 45 seconds respectively. If they changed together at 9 : 20 am, then when will they changed together next.

Options :

(A) at 9 : 23 : 45 an

(B) at 9 : 23 : 15 am

(C) at 9 : 23 : 30 am

(D) at 9 : 23 : 00 am

Given :-

• At two crossroads signal, light change after every 25 seconds and 45 seconds respectively. They changed together at 9 : 20 am.

To Find :-

• What is the time they will change together next.

Solution :-

First, we have to find the LCM of 25 and 45.

$\longmapsto$ $\sf 25 =\: 5 \times 5$

$\longmapsto$ $\sf 45 =\: 9 \times 5$

Then, the LCM of 25 and 45 is :

↦ 5 × 5 × 9

➦ 225

Hence, the LCM of 25 and 45 is 225.

⇒ 225 seconds

Then,

⇒ 3 minutes 45 seconds

Now, we have to find the new time they will change together is :

⇒ 9 : 20 + 3 minutes 45 seconds

➠ 9 : 23 : 45

$\therefore$ They will change together in 9 : 23 : 45 am.

Hence, the correct options is option no (A) at 9 : 23 : 45 am