Posted by **Rilee** on Friday, November 30, 2012 at 9:56pm.

A boat travels 1 km upstream and 1 km back. The time for the round trip is 4 hours. The speed of the stream is 5 km/hr. What is the speed of the boat in still water?

- Math -
**Reiny**, Friday, November 30, 2012 at 10:44pm
let speed of boat be x mph

time upstream = 1/(x-5)

time downstream = 1/(x+5)

1/(x-5) + 1/(x+5) = 4

multiply each term by (x+5)(x-5)

x+5 + x-5 = 4(x^2 - 25)

2x = 4x^2 - 100

4x^2 - 2x - 100 = 0

x = (2 ± √1604)/8

x = 5.256 or x = a negative, which would make no sense

the speed of the boat in still water is appr 5.26 mph

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