A boat can cover 40 km upstream and 60 km downstream together in 13 hours Also it can cover 50 km up...........

Quantitative Aptitude ( CCS) Boats and Streams

A boat can cover 40 km upstream and 60 km downstream together in 13 hours. Also it can cover 50 km upstream and 72 km downstream together in 16 hours. What is the speed of the boat in still water?

5.5 km/hr

6.5 km/hr

8.5 km/hr

3.5 km/hr

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Explanation:

Solution:
Upstream speed in both cases is 40 and 50. Ratio is 40 : 50 = 4 : 5. So let times in both cases be 4x and 5x
Downstream speed in both cases is 60 and 72 resp. Ratio is 60 : 72 = 5 : 6. So let times in both cases be 5y and 6y
So 4x + 5y = 13
and 5x + 6y = 16
Solve both, x = 2, y = 1
So upstream speed is = 40/4x = 5 km/hr
And downstream = 60/5y = 12 km/hr
So speed of boat is 1/2 * (5+12) = 8.5