Question

a motorboat whose speed is 15 km per hour in still water goes 30 km down stream and comes back in a total of 4 hours 30 minutes determine the speed of the stream

Answer 1

Let the speed of stream be x km/h
Speed downstream= (15+x)km/h
Speed upstream= (15-x)km/h
Therefore, 30/15+x + 30/15-x =4½
900/225-x²=9/2
9x²=225
x²=25
x= 5km/hr
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Answer 2

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 - x) km/hr.

Therefore,

30/(15+x) + 30/(15-x) = 4(1/2)

=> 900/(225-x^2) = 9/2

=> 9x^2 = 225

=> x^2 = 25

=> x = 5