A bat ,whose speed in still water is 16 km/hr . Covers a distance of 30 km in up stream and then returns taking 4 hours in total . What is the speed of current?
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Assume the stream’s speed to be 5km/h .
Downstream time = 30/20 = 1.5 h
Upstream time = 30/ 10 = 3h
Total time = 4.5 hours
And our assumption is correct.
Down stream time = 30/ ( 15 + v) = a
Upstream time = 30/ ( 15 -v) = b
a + b = 30*30/ (15^2 - v^2) = 4.5
Hence,
(15^2 - v^2) = 200
v = 5 km/h
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