# math algebra

A train averaged 80 km/h for the first half of its trip. How fast must it travel for the second half of the trip in order to average 96 km/h for the whole trip?

The answer is 120 km/ h but how do i set it up and get there? thanks for you help

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1. say it goes distance d in the first half (I assume half the distance, not half the time - poorly written question)

2 d = total distance = 96 T
t = time first half + time second half
T = t1 + t2
d = 80 t1
d = x t2
so
2d = 96 (t1+t2)
2d = 96 (d/80 + d/x)
2/96 = 1/80 +1/x
.02083 = .0125 + 1/x
1/x = .00833
I get x = 120

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posted by Damon

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