Question

A boat travels 30 km upstream in a river in the same amount of time as it takes to travel 60 km downstream. If the current of speed water is 4km/hr,find the speed of the boat in still water.

Answer 1

t speed in still water be x
A.T.Q
t=30/x-5 - (1)
t=50/x+5. -(2)
from 1&2
50/x+5=30/x-5
(50/x+5)-(30/x-5)=0
50x-250-30x+150/x²-25. =0
20x-100=x²-25
x²-20x+75=0
x²-15x-5x+75=0
x(x-15)-5(x-15)=0
(x-5)(x-15)=0
x=5 or15
x cant be 0
x=15km/hr

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