Question

Question #ba3d1

Answer 1

Each hour will get them `72+78=150` miles closer to each other.

Explanation:

So they will meet after `900div150=6` hours, or at `10"pm"` (on different tracks, I hope).

Answer 2

They pass after 6 hours, at `10` p.m.

Explanation:

This is a classic question involving distance, speed and time.

Recall `D = S xx T`

We know only one fact about each train that we are given.

One travels at `72` mph the other at `78` mph.

But the sum of the distance that each train travels is `900km`

The other fact is that the TIME travelled by each train until they pass each other will be the same.

We can use either of these to form an equation, but we need to define a variable first.

Let the time taken by the trains be `t` hours

For the first train, the distance travelled: `d_1= 72 xx t`
For the other train, the distance travelled: `d_2= 78 xx t`

The sum of these two distances is 900 miles:

`d_1+d_2 = 90`

`72t + 78t = 900`

`150t = 900`

`t = 6` hours

They pass each other 6 hours after leaving from the stations at 4 p.m. Therefore they pass at `4 + 6 = 10` p.m.