A man can row 5 km per hour in still water. If the river is flowing at 1km per hour, it takes him 75 minutes to row to a place and back. How far is the place ?
Solution
Correct Answer: Option A
Let, Distance = x
Man's speed u = 5 km/hr
stream's speed, v = 1 km/hr;
Time taken ( A→B) + Time taken (B←A) = Total time
=> x/u+v + x/u-v = 75/60 = 5/4
=> x/5+1 + x/5-1 = 5/4 => x/6+x/4 = 5/4
=> 2x+3x/12 = 5/4 => 5x/12 = 5/4 => x = 5×12/4×5
∴ x = 3 km
=> x/5+1 + x/5-1 = 5/4 => x/6+x/4 = 5/4
=> 2x+3x/12 = 5/4 => 5x/12 = 5/4 => x = 5×12/4×5
∴ x = 3 km
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