Question
A boat goes 200 km downstream in 50 hours, and 90 km
upstream in 30 hours. The speed of the stream isSolution
Distance downstream= 200 km Time taken to row downstream = 50 hrs. 
Speed downstream = 200/50= 4 km/hr. Distance upstream= 90 km, Time taken to row upstream = 30 hrs. Speed upstream =90/30= 3 km/hr. 
Speed of the stream = 1/2(4-3)= 1/2 km/hr
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