a man rows 750 seconds against the stream and returns in 7..., Problems On Boats & Streams, General Mathematics

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`

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+ AnswerC

+ ExplanationRate 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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