Let the speed of the boat in still water be ks and the speed of the stream be s
If d is the length of the one way, then time taken is
d/(ks+s) + d/(ks-s) = 2kd/((k^2-1) s)
if speed of boat in still water doubles, then
time taken would be 4kd/((4k^2-1) s)
The ratio of above two expressions is 8:3.2
Hence dividing the two
(4k^2 – 1)/ (k^2 – 1) = 5 solving for k, we get k^2 = 4 and hence k = 2, hence ratio is 2: 1.
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