alleryAverage speed for journey of equal distances at 60 km/h and 40 km/h:
A50
B50
C45
D48 km/h (harmonic mean: 2×60×40/(60+40) = 4800/100)
Answer & Solution
Correct answer: D. 48 km/h (harmonic mean: 2×60×40/(60+40) = 4800/100)
For equal distances, average speed = harmonic mean (NOT arithmetic).
We have HM = 2(60)(40)/(60+40).
That is HM = 4800/100.
So HM = 48 km/h.
Common CAT trap — average of speeds ≠ average speed.
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