Boats and Streams
- A boat running down stream covers a distance of 16 km in 2 hours while for covering the same distance upstream it takes 4 hours. What is the speed of the boat in still water ?
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From the question ,
Rate upstream = 16 kmph = 8 kmph 2 Rate downs tream = 16 kmph = 4 kmph 4 ∴ speed of boat in still water = 1 (Rate upstream + Rate downstream) 2
Correct Option: B
From the question ,
Rate upstream = 16 kmph = 8 kmph 2 Rate downs tream = 16 kmph = 4 kmph 4 ∴ speed of boat in still water = 1 (Rate upstream + Rate downstream) 2 speed of boat in still water = 1 (8 + 4) kmph = 6 kmph 2
- River is running at 2 kmph. It took a man twice as long to row up as to row down the river. The rate (in km ph) of the man in still water is :
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Let rate upstream be y kmph.
Then, rate downstream = 2y kmph∴ Rate of current = 1 (2y - y) = y kmph 2 2 ∴ y = 2 ⇒ y = 4 2
Correct Option: D
Let rate upstream be y kmph.
Then, rate downstream = 2y kmph∴ Rate of current = 1 (2y - y) = y kmph 2 2 ∴ y = 2 ⇒ y = 4 2
∴ Rate upstream = 4 kmph
Rate downstream = 8 kmph∴ Rate in still water = 1 (8 + 4) = 6 kmph 2
- A person can row a boat d km upstream and the same distance downstream
in 5 1 hrs Also he can row the boat 2d km upstream in 7 hours. He will row the 4
same distance downstream in
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Given that , Distance = d km
Let the speed of boat in still water be p kmph and that of current by q kmph.
According to the question,∴ d + d = 21 .........(i) p + q p - q 4 and 2d = 7 ⇒ d = 7 .........(ii) p - q p - q 2
By equation (ii) – (i),⇒ d = 21 - 7 = 21 - 14 = 7 p + q 4 2 4 4
Correct Option: A
Given that , Distance = d km
Let the speed of boat in still water be p kmph and that of current by q kmph.
According to the question,∴ d + d = 21 .........(i) p + q p - q 4 and 2d = 7 ⇒ d = 7 .........(ii) p - q p - q 2
By equation (ii) – (i),⇒ d = 21 - 7 = 21 - 14 = 7 p + q 4 2 4 4 ⇒ 2d = 7 = 3 1 hours. p + q 2 2
- A man rows to a place 48 km distance and back in 14 hours . He finds that he can row 4 km with the stream in the same time as 3 km against the stream. Find the rate of the stream ?
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Suppose that the man takes H hours to cover 4 km downstream and H house to cover 3 km upstream.
Then, 48H/4 + 48H/3 = 14Correct Option: A
Suppose that the man takes H hours to cover 4 km downstream and H house to cover 3 km upstream.
Then, 48H/4 + 48H/3 = 14
⇒ H = 1/2
∴ Rate upstream = 3/(1/2)= 6 km/hr
and rate downstream = 4/(1/2) = 8 km/hr
∴ Rate of the stream = (8 - 6)/2 = 1 km/hr .
