a Boat goes 40 km downstream and 30 km upstream 5 1/2 hours if the speed of the stream is 3 km per hour in what time can the boat goes 54 km downstream?
1)3 3/8
2) 4 1/2
3) 3 1/4
4) 3 1/2
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Answer:
speed of boat be -x
speed of boat in downstream = x +3
speed of boat in upstream= x -3
40/x+3 + 30/x-3 = 11/2
2(70x -30 ) = 11 ( x²-9)
140x -60 = 11x² - 99
11x² -140x -39=0
11x² -143x +3x -39= 0
11x ( x - 13) +3 ( x- 13) = 0
x= 13
speed of boat is 13 km/h
net speed in downstream is 16 km/h
time taken = 54/16
= 3 3/8 is ryt answer
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