1.

A person travels from A to B at a speed of 40 km/hr and returns by increasing his speed by 50%. What is his average speed for both the trips?

Answer»

48 km/hr



Method : 1
If a car covers a CERTAIN distance atxkmph and an equal distance at y kmph,
the average SPEED of the whole journey = 2xy/x+y kmph.
By using the same formula, we can find out the average speed quickly
Speed with which he travels from A to B = x = 40 km/hr
Speed with which he travels from B to A = x = 40×(100+50)/100 = 60 km/hr
average speed = (2×40×60)/(40+60) = 48 km/hr

Assume that distance from A to B = x km

Speed with which he travels from A to B = x = 40 km/hr

Time to travel from A to B = distance/speed = x/40 hr

Speed with which he travels from B to A = 40×(100+50)/100 = 60 km/hr

Time to travel from B to A = distance/speed = x/60

Total distance traveled = x+x = 2X

Total time taken = x/40 + x/60

Average speed = Total distance traveled/Total time taken = 2x/(x/44)+(x/60)

= 2/[(1/60)+(1/40)] = (2×2400)/(40+60) = 2×24 = 48 km/hr


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