Question
If the speed of stream is 3 km/h, a boat takes 9 hours
to travel 112 km downstream and 110 km upstream. What is the speed (in km/h) of the boat in still water?Solution
Given: Stream speed = 3 km/h Downstream: 112 km Upstream: 110 km Total time = 9 hours Let boat speed in still water = x km/h Downstream speed = x + 3 Upstream speed = x − 3 Time = Distance / Speed 
Multiply both sides by (x + 3)(x − 3): 
Solve using quadratic formula: 
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