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Shortcut:
If a km/hr be the man's rate in still water, then a =
1
/
2
(man's rate with current + his rate against current)
Downstream speed =
44
/
4
= 11 km/hr
Here, a = 8, upstream speed = z, downstream speed = 11
Using these values in the shortcut, we get:
8 =
1
/
2
(11 + z)
8 x 2 = 11 + z
16 = 11 + z
z = 16 − 11 = 5
km/hr
Hence, upstream speed = 5 km/hr
⇒ 5 km in 1 hour
Hence, 25 km will be covered in 5 hour.

