A person rows a distance of 20 km upstream and 15 km downstream in a total time of \(2 \frac{5}{12}\) hours. If the speed of the current is 4 km/h, then in how many hours can he row a distance of 64 km upstream?

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SBI PO Prelims 1 Nov 2023 Memory Based Paper (Shift 1)

\(5 \frac{1}{3}\)
\(4\frac{2}{3}\)
\(5\frac{1}{2}\)
\(4\frac{1}{4}\)
\(4\frac{1}{5}\)

Answer 1

Given:

A person rows a distance of 20 km upstream and 15 km downstream in a total time of 2(5/12) hours

Speed of the current is 4 km/h

Formula used:

Distance = speed × time

Speed in downstream = speed of the boat + speed of the stream

Speed in upstream = speed of the boat - the speed of the stream

Calculation:

Let the speed of the boat be 'x' km/h

Speed in downstream = x + 4 km/h

Speed in upstream = x - 4 km/h

Now ,

Time taken in downstream = 15/(x + 4) hours

Time taken in upstream = 20/(x - 4) hours

Total time = time of upstream + time of downstream

⇒ 2(5/12) = [15 /(x + 4)] + [20/(x - 4)]

⇒ x = 16

Now time taken to cover 64 km in upstream

Time = 64/(x -4)

⇒ 64(/16 - 4) = 64/12

⇒ 16/3 hours

∴ Boat will take 16/3 hours to complete 64 km in upstream.