# Algebra

A bus covered the 400-km distance between points A and B at a certain speed. On the way back the bus traveled at the same speed for 2 hours and then increased the speed by 10 km/hour until it reached A, thus spending 20 fewer minutes on the return trip. How long did the return trip take?

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1. from A to B at speed s took h hours.

s*h = 400

on the way back,

s*2 + (s+10)(h-2 - 1/3) = 400
h=5, so A to B took 5 hours.
so, ...

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posted by Steve

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