Jyoti can row a boat at $7\frac{1}{2}$ km/h in still water. If in a river running at 1.5 km/h, she takes 50 minutes to row to a place A and come back, then how far off is the place A?
Answer & explanation
Correct answer: option 1
Jyoti's Speed in still water = 7 1/2 km/h
River's speed 1.5 km/hr
Assume she goes to Distance "D" in upstream and downstream each
Upstream Velocity = 7.5-1.5 = 6 km/hr
Downstream velocity = 7.5+1.5 = 9 km/hr
Time taken to row Upstream, T1 = D/(6)
Time taken to row Downstream, T2 = D/(9)
T1 + T2 = 5/6
D/6 + D/9 = 5/6
(3D+2D)/18 = 5/6
5D = 15
The correct answer is Option (1) → 3 km