Question
The Speed of the ship in calm water is five times the
speed of the stream. If the ship can travel 's + 30' km downstream or 's - 10' km upstream in 5 hours, determine the time it takes for the ship to cover '4s - 170' km in still water.Solution
ATQ, Downstream speed of the Ship = (s + 30)/5 = ‘0.2s + 6’ km/h Upstream speed of the Ship= (s – 10)/5 = ‘0.2s – 2’ km/h Speed of the stream = (0.2s + 6 – 0.2s + 2)/2 = 4 km/h Speed of the ship in still water = 5 × 4 = 20 km/h According to question: 0.2s + 6 = 20 + 4 0.2s = 18 s = 90 So the time taken by the ship to cover ‘4s – 170’ km in still water = (4 × 90 – 170)/20 = 9.5 hours = 9 hours 30 minutes
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