Question
The downstream and upstream speeds of a boat are 36 km/hr
and 28 km/hr, respectively. If the boatman covers (x + y) km upstream in 8 hours while the stream flows at double its usual speed, find 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) = 36 … (i)
Also, (B – s) = 28 … (ii)
Solving equation (i), and (ii), we get,
B = 32 km/hour
s = 4 km/hour
According to question,
(x + y)/(B – 2s) = 8
(x + y) = 8 × (32 – 2 × 4) = 8 × 24 = 192 km
Therefore, average value of x and y = (x + y)/2 = 192/2 = 96 km
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