Question

A fisherman can row a boat 8km downstream and return in100 minutes if the speed of the stream is 2km/hr find the speed of boat in still water

Answer 1

speed of the stream = 2 km/hr
let speed of the boat in still water be x km/hr

Time taken to travel downstream = 8/(x+2)
Time taken to travel upstream = 8/(x-2)

Total time = 1 hr 40 min = 5/3 hr
8(x+2)+8(x−2)=538(x+2)+8(x−2)=53

24(x- 2) + 24(x+2)  = 5(x+2)(x-2)
48x = 5x2 - 20
5x2 - 48x -20=0

x =  48±√(−48)2−4×5×(−20)2×548±(−48)2−4×5×(−20)2×5

=48±√2304+40010=48±2304+40010  

=48±5210=48±5210 

= 10 (taking only the positive value)

i.e., speed of the boat in still water = 10 km/hr 

Answer 2

Answer:

Speed of boat in still water =10 km/h

Step-by-step explanation: