Swati can row a boat on still water at a speed of 5 km/hr. However, on a given river, it takes her 1 hour more

Question

Swati can row a boat on still water at a speed of 5 km/hr. However, on a given river, it takes her 1 hour more to row the boat 12 km upstream than downstream. One day, Swati rows the boat on this river from X to Y, which is N km upstream from X. Then she rows back to X immediately. If she takes at least 2 hours to complete this round trip, what is the minimum possible value of N?

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Accepted Answer

4.8. Let the speed of the stream be x 12 5 − x = 12 5 + x + 1 \frac{12}{5-x}=\frac{12}{5+x}+1 5 − x 12 ​ = 5 + x 12 ​ + 1 The value of x satisfying the above equation is 1 Now, N 5 + 1 + N 5 − 1 ≥ 2 \frac{N}{5+1}+\frac{N}{5-1}\ge2 5 + 1 N ​ + 5 − 1 N ​ ≥ 2 2 N + 3 N 12 ≥ 2 \frac{2N+3N}{12}\ge2 12 2 N + 3