71. A
man can row 18 kmph in still water. It takes him thrice as long to row up as to
row down the river. Find the rate of stream.
A.)
5 km/hr.
B.)
9 km/hr.
C.)
15 km/hr.
D.)
22 km/hr.
Answer: Option B
Explanation:
Let man’s rate upstream be x kmph.
Then, his rate downstream = 3x kmph
Rate in still water = 1/2 (3x + x) kmph = 2x kmph
So, 2x = 18 or x = 9
Rate upstream = 9 km/hr, Rate downstream = 27 km/hr
Hence, rate of stream = 1/2 (27 – 9) km/hr = 9 km/hr
