Answers

2014-06-04T17:50:53+05:30
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)
2 2 2