Question
A boat takes 3 hours to travel 36 km downstream and 4 hours to travel 24 km upstream. If the speed of the boat in still water is increased by 2 km/h, what will be its new speed in still water?
Solution
Let speed of boat in still water = b km/h Let speed of current = c km/h Downstream speed = b + c Upstream speed = b − c Downstream: 36 / (b + c) = 3 ⇒ b + c = 12 Upstream: 24 / (b − c) = 4 ⇒ b − c = 6 Add both: (b + c) + (b − c) = 12 + 6 2b = 18 b = 9 km/h New still water speed = b + 2 = 9 + 2 = 11 km/h
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