Question

A man rows a boat 18 kilometres in 4 hours down-stream and returns upstream in 12 hours. The speed of the stream (in km per hour) is :

• A. 1
• B. 1.5
• C. 2
• D. 1.75

Answer 1

Answer:

B. 1.5

Solution:

Rate downstream U_s$=\frac{18}{4}=\frac{9}{2}kmph$

Rate upstream D_s $=\frac{18}{12}=\frac{3}{2}kmph$

Now, speed of the stream $=\frac{D-U}{2}$

$=\frac{\frac{9}{2}-\frac{3}{2}}{2}$

$=\frac{6}{4}=\frac{3}{2}=1.5 kmph$

Speed of Stream = 1.5 kmph.