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If A travels a certain distance at a speed of x km/ hour and an equal distance at a speed of y km/hour, then average speed of a for the whole journey must be:-
(a)Arithmetic Mean of x and y.
(b)Geometric Mean of x and y.
(c)Harmonic Mean of x and y.
(d)None or the above.
Harmonic Mean of x and y.
Please explain your answer.
Well first of all i dont think its a brain teaser at all.
Let the distance = d
time taken at speed x, t1= = d/x
time taken at speed y, t2 = d/y
Average speed = Total distance/Total Time
= (d +d) / (t1 + t2)
= 2d/(d/x + d/y)
=2xy/(x+y)
which is the Harmonic mean of x and y