A man rows to a certain place and comes back but by mistake he covers 1 3rd more distance while comi...........

Quantitative Aptitude ( CCS) Boats and Streams

A man rows to a certain place and comes back, but by mistake he covers 1/3rd more distance while coming back. The total time for this journey is 10 hours. The ratio of speed of boat to that of stream is 2 : 1. If the difference between upstream and downstream speed is 12km/hr, then how much time will the man take to reach to starting point from his present position?

35 minutes

45 minutes

60 minutes

40 minutes

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Explanation:

Solution:
Speed of boat and stream – 2x and x respectively. So downstream speed = 2x+x = 3x, and upstream speed = 2x-x = x
Let total distance between points is d km
So he covered d km downstream, and while coming back i.e. upstream he covers d + 1/3 *d = 4d/3 km
Total time for this journey is 10 hrs. So
d/3x + (4d/3)/x = 10
Solve, d = 6x
Now also given, that (2x+x) – (2x-x) = 12
Solve, x = 6
So d = 36 km
So to come to original point, he will have to cover 1/3 * 36 = 12 km
And with speed 3x = 18 km/hr(downstream)
So time is 12/18 * 60 = 40 minutes