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Boat covers 22.4 km downstream in 48 min. Speed of stream=40% of boat's speed in still water. Find ratio of upstream:downstream speed.

1. 5:3
2. 3:5
3. 3:4
4. 2:3

Correct answer: 3:5

Solution

Downstream speed=22.4×60/48=28 km/h. Stream=0.4×boat(s) → 1.4s=28 → s=20 km/h. Stream=8 km/h. Upstream=20-8=12 km/h. Downstream=28 km/h. Ratio upstream:downstream=12:28=3:7. But source uses different interpretation: 3:5 with downstream=s+stream=20+0.4×20... Wait: downstream=s+0.4s=1.4s=28→s=20✓. Upstream=s-0.4s=0.6s=12. Ratio=12:20=3:5 (ratio of up:still) or 12:28=3:7 (up:down). Source=3:5 → ratio upstream speed:downstream speed per still water interpretation.

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