A rows a boat 100km in 20 hours downstream and 72km in upstream in 18 hours. Find the speed of the boat in still water?
Answers
Answered by
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Explanation:
downstream speed = 100/20 = 5 km/hr
upstream speed = 72/18 = 4 km/hr
speed of boat in still water = 1/2*(5+4)
= 4.5 km/hr
Answered by
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Answer:
The speed of the boat in still water us 4.5 km/h
Explanation:
Let the speed of the boat in still water is u km/h
and the speed of the river is v km/h
Then,
The speed of the boat downstream = u+v
Speed of the boat upstream = u-v
using Time = Distance/Speed
Time taken downstream = Distance/Downstrem Speed
or, 20 = 100/(u+v)
⇒ u+v = 100/20
⇒ u+v = 5 .................... (1)
Time taken upstream = Distance/Upstrem Speed
or, 18 = 72/(u-v)
⇒ u-v = 72/18
⇒ u-v = 4 .................... (2)
Adding eq (1) and eq (2) we get
2u = 9
or, u = 9/2 = 4.5
Therefore, the speed of the boat in still water us 4.5 km/h
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