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A boat travels 20 km upstream in 10 hours and 72 km downstream in 8 hours. What is the speed of a boat in still water?
1. 5.5 kmph
2. 11/7 kmph
3. 6 kmph
4. 5 kmph

1 Answer

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Best answer
Correct Answer - Option 1 : 5.5 kmph

Given:

u/s = 20 km in 10 hours

Ds = 72 kms in 8 hours

Formula used:

If speed in upstream in X kmph and downstream is Y kmph

Speed in still water = (1/2)(X + Y) kmph

Rate of stream = (1/2)(X – Y) kmph

Calculations:

Speed of upstream and downstream

⇒ Speed of upstream = 20 / 10

⇒ Speed of upstream = 2 kmph

⇒ Speed of downstream = 72 / 8

⇒ Speed of downstream = 9 kmph

⇒ speed in still water = (1/2)(2 + 9)

⇒ Speed in still water = 11/2 kmph

Speed in still water is 5.5 kmph

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