Question
There is road beside river. Two friends started from a
point A, moved to a school situated at another point B and then returned to A again. One of them moves on a motorcycle at a speed of 24km/hr, while the other sails on a boat at a speed of 20km/hr. If the river flows at the speed of 8km/hr, which of the two friends will return to point A first?(flow of the river is from point A to B)Solution
Clearly, the motorcyclist move both ways at a speed of 24km/hr. So, average speed of the motorcyclist = 24km/hr The boat sail or moves downstream = 20 + 8 = 28 km/hr Boat sail or moves upstream = 20 – 8 = 12 km/hr So, average of the boat = (2 × 28 × 12 )/(28 + 12) = 672/40 = 16.8 km/hr Since, the average speed of the motorcyclist is greater, he will return to A first.
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