Question

A man rows to a place 60 km distant and come back in 35 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. Find the speed in still water and in stream:

• A. 1.5, 2
• B. 0.5, 2.5
• C. 3.5, 0.5
• D. 2, 2.5

Answer 1

Answer:

C. 3.5, 0.5

Explanation:

  If he moves 4 km downstream in x hours.

Downstream speed $=\frac{4}{x}$

Upstream speed $=\frac{3}{x}$

Then $\frac{60}{(\frac{4}{x})} +\frac{60}{(\frac{3}{x})}=35$

$60[\frac{(3x+4x)}{12}]=35$

$60\times{\frac{7x}{12}}=35$

$5\times{7x} = 35$==> x=1km.

Then Downstream speed=4km/hr ,

Upstream speed=3km/hr

U $=\frac{(4+3)}{2}=\frac{7}{2}=3.5km/hr$

V=$\frac{(4-3)}{2}=\frac{1}{2}=0.5km/hr$