Robert C. answered • 09/25/12

Dr. Robert can help you with Math and Science

The answer is not 2 hours.

The trains will meet up when the first train has been going for 3 hours and the second train has been going for 2.5 hours. Each will have travelled 180 miles at that point in time.

t is the time that the first train has been traveling in hours.

t-0.5 is the time that the second train has been traveling in hours.

Distance that the first train travels during that time is

t*60

Distance that the second train travels is

(t-0.5)*72

The two trains are at the same distance when those two expressions are equal

t*60 = (t-0.5)*72

60t = 72t-36

36 = 12t

3 = t

I hope that helps.

FREDERICK S.

That should help, Robert, because you laid out all the steps.

The most important thing for this student to learn is that distance - rate*time

and the units must be compatible - minutes or hours on time; distance in miles, let's say; and thus - if hours are used - rate is in miles per hour.

IF they can manage all this, there is no stopping the trains!

[I hope there are two tracks or the secod one runs into the first one!]

Good work.

10/19/12