Question
The speed of a boat while moving downstream is 80% higher than its speed while moving upstream. If the boat covers a distance of 720 km downstream in 20 hours, determine the speed of the boat in still water.
Solution
ATQ;
Let speed of the boat in still water and speed of stream be ‘x’ km/h and ‘y’ km/h, respectively.
Downstream speed of the boat = (x + y) km/h
Upstream speed of the boat = (x – y) km/h
Downstream speed of the boat = (720/20) = 36 km/h
ATQ,
(x + y) = 36 ------- (I)
And, 36 = 1.8 × (x – y)
Or, (x – y) = 20 -------- (II)
By adding equation (I) and equation (II), we get
x = 28
Therefore, speed of boat in still water = 28 km/h
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