Question 915785
One train goes 90 km from town a to town b.
Another train takes 2.5 hours longer to travel the same distance at 50 km per hour. 
How far away are the two towns?
:
let d = distance between the towns
:
Write a time equation; time = dist/speed
50km/h time - 90km/h time = 2.5 hrs
{{{d/50}}} - {{{d/90}}} = 2.5
multiply equation by 450 to get rid of the denominators
450*{{{d/50}}} - 450*{{{d/90}}} = 450*2.5
Cancel the denominators and we have
9d - 5d = 1125
d = 1125/4
d = 281.25 km
:
:
See if that checks out, find the actual time at each speed
281.25/50 = 5.625 hrs
281.25/90 = 3.125 hrs
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difference: 2.500 hrs