Problems On Boats & Streams, General Mathematics

Question: If a man can swim downstream at `6` kmph and upstream at `2` kmph his speed in still water is :
A
`4 km∕hr`

B
`2 km∕hr`

C
`3 km∕hr`

D
` 2.5 km∕hr`

Note: Speed in still water `= 1/2 (6 + 2) kmph` `= 4 kmph`
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Question: A man rows `750` seconds against the stream and returns in `7 1/2` minutes. His rowing speed in still water is :
A
`3 km∕hr`

B
`4 km∕hr`

C
`5 km∕hr`

D
`6 km∕hr`

Note: Rate upstream `= (750/675) m∕sec` `= 10/9 m∕sec` Rate downstream `= (750/450) m∕sec` `= 5/3 m∕sec.` Rate in still water `= 1/2 (10/9 + 5/3) m/sec` `= 25/18 m∕sec.` `= (25/18 xx 18/5) kmph` `= 5 kmph.`
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Question: If a boat goes `7` km upstream in `42` minutes and the speed of the stream is `3` kmph, then the speed of the boat in still water is :
A
`4.2 km/hr`

B
`9 km/hr`

C
`13 km/hr`

D
`21 km/hr`

Note: Rate upstream `= (7/42 xx 60) kmph` `= 10 kmph` Speed of stream `= 3 kmph` Let speed in still water be x km/hr Then, speed upstream `= (x - 3) km/hr` `:. x - 3 = 10` ` or x = 13 kmph`
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Question: A man can row `9 1/3` kmph in still water and finds that it takes him thrice as much time to row up than as to row down the same distance of in the river. The speed of the current is :
A
`3 1/3 km∕hr`

B
`3 1/9 km∕hr`

C
`4 2/3 km∕hr`

D
`14 km∕hr`

Note: Let speed upstream be x kmph Then, speed downstream`= 3x kmph` :. Speed in still water `= 1/2 (3x + x) kmph` `= 2x kmph` `:. 2x = 28/3 ⇒ x = 14/3` :. speed upstream`= 14/3 km/hr,` Speed downstream`= 14 km∕hr` :. Speed of the current`= 1/2 (14 - 14/3) km/hr` `= 14/3 km∕hr` `= 4 2/3 km∕hr`
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Question: A man can row a boat at `10` kmph in still water. If the speed of the stream is `6` kmph , the time taken to row a distance of `80` km down the stream is :
A
`8 hours`

B
`5 hours`

C
`10 hours`

D
`20 hours`

Note: Speed downstream `= (10 + 6) km/hr` `= 16 km/hr` Time taken to cover `80` km downstream `= (80/16) hrs` `= 5 hrs`
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Question: A boat takes `4` hours for travelling downstream from point A to point B and coming back to point A upstream. If the velocity of the stream is `2` kmph and the speed of the speed of the boat in still water is `4` kmph, what is the distance between A and B ?
A
`4 kms`

B
`6 km`

C
`8 km`

D
`9 km`

Note: Let the distance between A and B x hm. Speed downstream`= 6` kmph, speed upstream`= 2 kmph` `:.x/6 + x/2 = 4 ⇔ 4x = 24 ⇔ x = 6` :. Distance AB`= 6 km.`
1. Report
Question: If a man rows at `6` kmph in still water and `4.5`kmph against the current then his rate along the current is :
A
`9.5 km/hr`

B
`7.5 km/hr`

C
`7 km/hr`

D
`5.25 km/hr`

Note: Let the rate of the stream be x kmph Then, rate against the current `= (6 - x) kmph` `:. 6 - x = 4.5` `or x = 1.5` :. Rate of current `= 1.5 kmph` Rate along the current `= (6 + 1.5) kmph = 7.5 kmph`
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Question: If a man,s rate with the current is `11` kmph and the rate of the current is `1.5` kmph, then the man,s rate against the current is :
A
`8 km/hr`

B
`9.5 km/hr`

C
`9 km/hr`

D
`6.25 km/hr`

Note: Man,s rate in still water `= (11 - 1.5) kmph` `= 9.5 kmph` Man,s rate against the current `= (9.5 - 1.5) kmph` `= 8 kmph`
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Question: Speed of a boat in standing water is `9` kmph and the speed of the stream is `1.5` kmph. A man rows to a place at a distance of `10.5` km and comes back to the starting point. The total time taken by him is :
A
`16 hours`

B
`18 hours`

C
`20 hours`

D
`24 hours`

Note: Speed upstream `= 7.5 kmph,` speed downstream `= 10.5 kmph` :. Total time taken `= (105/7.5 + 105/10.5) hrs` `= 24 hours.`
1. Report
Question: A boat moves upstream at the rate of `1` km in `10` minutes and downstream at the rate of `1` km in `6` minutes. The speed of the current is :
A
`1 km∕hr`

B
`1.5 km∕hr`

C
`2 km∕hr`

D
`2.5 km∕hr`

Note: Rate upstream `= (1/10 xx 60) km∕hr` `= 6 km∕hr` Rate downstream `= (1/6 xx 60) km∕hr` `= 10 km∕hr` Rate of the current `= 1/2 (10 - 6) km∕hr` `= 2 km∕hr`
1. Report

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Question: If a man can swim downstream at `6` kmph and upstream at `2` kmph his speed in still water is :

Question: A man rows `750` seconds against the stream and returns in `7 1/2` minutes. His rowing speed in still water is :

Question: If a boat goes `7` km upstream in `42` minutes and the speed of the stream is `3` kmph, then the speed of the boat in still water is :

Question: A man can row `9 1/3` kmph in still water and finds that it takes him thrice as much time to row up than as to row down the same distance of in the river. The speed of the current is :

Question: A man can row a boat at `10` kmph in still water. If the speed of the stream is `6` kmph , the time taken to row a distance of `80` km down the stream is :

Question: A boat takes `4` hours for travelling downstream from point A to point B and coming back to point A upstream. If the velocity of the stream is `2` kmph and the speed of the speed of the boat in still water is `4` kmph, what is the distance between A and B ?

Question: If a man rows at `6` kmph in still water and `4.5`kmph against the current then his rate along the current is :

Question: If a man,s rate with the current is `11` kmph and the rate of the current is `1.5` kmph, then the man,s rate against the current is :

Question: Speed of a boat in standing water is `9` kmph and the speed of the stream is `1.5` kmph. A man rows to a place at a distance of `10.5` km and comes back to the starting point. The total time taken by him is :

Question: A boat moves upstream at the rate of `1` km in `10` minutes and downstream at the rate of `1` km in `6` minutes. The speed of the current is :