Question 205892
A cyclist travels 80km from Paris to Louvre at an average speed of x km/h.  Find the time taken in term of x.
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t1 = 80/x hours
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On his return journey from Louvre to Paris, he decreases his average speed by 3km/h. Find the time taken on the return journey in terms of x. 
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t2 = 80/(x-3) hours
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If the difference between the times is one hour 20 minutes, find the value of x.
t1-t2 = 4/3 hours
80/x - 80/(x-3) = 4/3
Multiply thru by x(x-3)*3
80*(x-3)*3 - 80x*3 = 4x*(x-3)
240x-720 - 240x = 4x^2-12x
4x^2-12x+720 = 0
x^2-3x+180 = 0
(x-15)*(x+12) = 0
x = -12 kph (Ignore)
x = 15 khp