Question

A man can row 30 km down stream and return in a total of 8 hours. If the speed of the boat in still water is four times the speed of the current, then the speed of the current is

• A. 1 kmph
• B. 2 kmph
• C. 4 kmph
• D. 3 kmph

Answer 1

Answer:

B. 2 kmph

Let the speed of stream be x kmph

then speed of boat in still water = 4x kmph

Rate downstream = 4x + x = 5x kmph

Rate upstream = 4x – x = 3x kmph

$\frac{30}{3x}+\frac{30}{5x}=8$

$\frac{10}{x}+\frac{6}{x}=8$

$\frac{16}{x}=8$

$x= 2kmph$