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.

Correct result:

v =  7.5 km/h

Solution:

s=100 km t1=4 h t2=10 h    s=t1 (a+v) s=t2 (av) 100=4 (a+v) 100=10 (av)  4a+4v=100 10a10v=100  a=352=17.5 v=152=7.5=152 km/h=7.5 km/h



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