98.The
current of a stream runs at the rate of 2 km per hr. A motor boat goes 10 km
upstreams and back again to the starting point in 55 min. Find the speed of the
motor boat in still water?
[A]
22
[C]
25
[B]
23
[D]
24
Answer : [A]
Explanation :
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Let
the speed of boat in still water be x kmph
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Speed
downward = (x + 2) kmph
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Speed
upstream = (x – 2) kmph
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Time
taken to row 10 kms and back =
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10
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+
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10
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hrs
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x + 2
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x - 2
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10
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+
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10
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=
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55
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(or)
11x2 - 240x - 44 = 0
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x + 2
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x - 2
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60
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(or)
11x2 - 242x + 2x - 44 = 0
(or) (x - 22) (11x + 2) = 0
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x =
22
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Hence
speed of motor boat in still water is 22 kmph
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