Question
A boat goes downstream at 28 km/hr and upstream at 20
km/hr. If it takes 14 hours to travel (x + y) km upstream when the stream speed is doubled, then what is the average of x and y?Solution
ATQ,
Let, speed of boat in still water and stream speed be B km/hour and s km/hour, respectively.
So, (B + s) = 28 … (i)
Also, (B – s) = 20 … (ii)
Solving equation (i), and (ii), we get,
B = 24 km/hour
s = 4 km/hour
According to question,
(x + y)/(B – 2s) = 14
(x + y) = 14 × (24 – 2 × 4) = 14 × 16 = 224 km
Therefore, average value of x and y = (x + y)/2 = 224/2 = 112 km
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