Question
A boat can move downstream at 30 km/h and upstream at 18
km/h. If it takes the boatman 10 hours to travel a total of (p + q) km upstream when the stream current is double the usual, calculate the average of 'p' and 'q'.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) B - s = 18 … (ii) Solving equation (i) and (ii), we get, B = 24 km/hour s = 6 km/hour According to the question, (p + q)/(B - 2s) = 10 (p + q) = 10 × (24 - 2 × 6) = 10 × 12 = 120 km Therefore, average value of p and q = (p + q)/2 = 120/2 = 60 km
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