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View Answer
Shortcut:
If a km/hr be the rate of the current, then a =
1
/
2
(man's rate with current − his rate against current)
Rate upstream =
3
/
4
x
60
/
15/2
=
3
/
4
x
60 x 2
/
15
= 6 km/hr
Rate downstream =
3
/
4
x
60
/
15/4
=
3
/
4
x
60 x 4
/
15
= 12 km/hr
Here, upstream speed = 6, downstream speed = 12, a = ?
Using these values in the shortcut, we get:
a =
1
/
2
(12 − 6)
a =
1
/
2
x 6 = 3
Hence, the rate of stream is 3km/hr.
Speed in still water =
1
/
2
(12 + 6)
=
1
/
2
x 18 = 9
Hence, the speed in still water is 9 km/hr.
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