A man can row three-quarters of a kilometre against the stream in 11¼ minutes and down the stream in 7½ minutes. The speed (in km/hr) of the man in still water is:

2
3
4
5

Correct Answer: 5

Explanation:

We can write three-quarters of a kilometre as 750 metres,

and 11¼ minutes as 675 seconds.

Rate upstream =	❨	750	❩m/sec	=	10	m/sec.
		675			9

Rate downstream =	❨	750	❩m/sec	=	5	m/sec.
		450			3

∴ Rate in still water =	1	❨	10	+	5	❩m/sec
	2		9		3

=	25	m/sec
	18

=	❨	25	x	18	❩km/hr
		18		5

= 5 km/hr.

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