Question

A Boat goes 12 km upstream and 40 km downstream in 8 hours it can go 16 km upstream and 32 km downstream in same time find the speed of a of a boat in still water if speed of the stream 2 kilometre per hour

Answer 1

let speed of boat is x and stream is y
speed of boat upstream = x-y
speed of boat downstream = x+y
8 = 12/(x-y) + 40/(x+y)
8(x²-y²) = 52x -28y ..................(1)
8 = 16/(x-y) + 32/(x+y)
8(x²-y²) = 48x - 16y ..................(2)
(1) - (2)
4x - 12y = 0
x = 3y  .........................(3)   put in equation (1)
8(9y²-y²) = 52*3y - 28y
64y² = 128y
y = 0 or 2
y= 0 not possible 
put y = 2 in equation (3)
x = 6Km./h   (speed of boat in still water)
y = 2Km./h   (speed of stream)
HOPE THIS WILL HELP U
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