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Question
A sailor goes 8 km downstream in 420 minutes and returns in 1 hour. Find the speed of the sailor in still water and the speed of the current .
Solution
Let the speed of the sailor in still water be x km/h and that of the current y km/h.
Speed downstream = (x + y) km/h
Speed upstream = (x – y) km/h
As per the question
(x + y) × `40/60` = 8
⇒ x + y = 12 ………(i)
When the sailor goes upstream, then
(x – y) × 1 = 8
x – y = 8 ………(ii)
Adding (i) and (ii), we get
2x = 20 ⇒ x = 10
Putting x = 10 in (i), we have
10 + y = 12 ⇒ y = 2
Hence, the speeds of the sailor in still water and the current are 10 km/h and 2 km/h respectively.
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