M7MBA wrote:If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?

A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.

The OA is A.

I don't know how to solve this PS question. Experts, could you tell me how? Please.

They are approaching each other at a combined speed of 72+48 = 120 mph = 2 miles/minute.

So, since they are 1 minute apart according to the question, at their combined speed of 2 miles/minute:

distance = rate x time > = 2 miles/minute x 1minute = 2 miles A

Hello M7MBA.

It is easier and faster as regor60 said.

But if you don't know about the combine speed, you can solve it as follows.

Train A travels at 48mph, which is equivalent to 48/60=4/5 miles per minute.

Train B travels at 72mph, which is equivalent to 72/60=6/5 miles per minute.

Suppose that you're in the place where they collisioned.

If you go back 1 minute, then train A move back 4/5 miles and train B moves back 6/5 miles.

So, their distance is equal to 4/5+6/5=10/5=2 miles.

So, the correct answer is A.

I hope this explanation may help you.

I'm available if you'd like a follow up.

M7MBA wrote:If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?

A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.

Since the trains travel toward each other, they WORK TOGETHER to cover the distance between them.
When elements work together, ADD THEIR RATES.
Combined rate for the two trains = 72+48 = 120 miles per hour = 2 miles per minute.

Let the TOTAL travel time for the two trains = 1 minute.
Let the faster train start at Point A and the slower train start at Point B.
The question stem becomes:
If it takes 1 minute for the two trains to meet, what is the distance between Point A and Point B?
Since the two trains travel at a combined rate of 2 miles per minute for a total time of 1 minute, the distance between Point A and Point B = rt = 2*1 = 2 miles.

The correct answer is A.