Question

A man can row three quarters of a km against the stream in 11 minutes 15 seconds ad return in 7 minutes 30 seconds. Find the speed of the man in still water and also the speed of the stream
(a) 5 km/hr, 2 km/hr
(b) 5 km/hr, 1 km/hr
(c) 6 km/hr, 2 km/hr
(d) 4 km/hr, 1 km/hr
(e) None of these

Answer 1

the answer is b. We can write three-quarters of a kilometre as 750 metres,

and 11 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.

Answer 2

Answer:

The correct answer for this problem is option (b) 5km/hr , 1km/hr

Step-by-step explanation:

11 minutes 15 secs in seconds = 11*60 + 15 => 675 seconds

7 minutes 30 secs in seconds = 7*60 + 30 => 450 seconds

Three quarters of a km => 3/4 km

For Downstream ->

(3/4) / 675/3600 = B - S  (Three quarters in km/hr)

4 = B - S

For Upstream  ->

(3/4) / 450/3600 = B - S

6 = B + S

Speed of man (or speed of boat) -->

B = (4 + 6) / 2 => 5km/hr

Speed of stream -->

S = (6 - 4) / 2 => 1km/hr

hence, option (b) is correct option.