A man can row 50 km upstream and 72 km downstream in 9 hours. He can also row 70 km upstream and 90 km downstream in 12 hours. Find the rate of current.	Choose the most appropriate option.
A) 8 kmph  B) 3 kmph  C) 6 kmph  D) 4 kmph  E) None of these
Let x and y be the upstream and downstream speed respectively.   Hence, 50/x + 72/y = 9 and 70/x + 90/y = 12   Solving for x and y we get x = 10 km/hr and y = 18 km/hr   We know that Speed of the stream = 1/2 * (downstream speed - upstream speed) = 1/2 (18 - 10) = 4 km/hr.   ANSWER:4 kmph
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A man can row 50 km upstream and 72 km downstream in 9 hours. He can also row 70 km upstream and 90 km downstream in 12 hours. Find the rate of current.