# Water current speed.

Two cities along the river are 100 km apart. The powerboat downstream runs for 4 hours, upstream for 10 hours. Determines the river's current speed.

Result

v =  7.5 km/h

#### Solution:

100 = 4*(a+v)
100 = 10*(a-v)

4a+4v = 100
10a-10v = 100

a = 352 = 17.5
v = 152 = 7.5

Calculated by our linear equations calculator.

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