Question
If a boat's downstream and upstream speeds are 30 km/hr
and 22 km/hr respectively, and it travels (x + y) km upstream in 10 hours when the stream speed is twice the regular one, 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) = 30 … (i)
Also, (B – s) = 22 … (ii)
Solving equation (i), and (ii), we get,
B = 26 km/hour
s = 4 km/hour
According to question,
(x + y)/(B – 2s) = 10
(x + y) = 10 × (26 – 2 × 4) = 10 × 18 = 180 km
Therefore, average value of x and y = (x + y)/2 = 180/2 = 90 km
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