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Q150
(IAS/2001)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Quantitative aptitude topics
Answer Verified
A person travels from X to Y a speed of 40 kmph and returns by increasing his speed by 50%. What is his average speed for both the trips ?
Result
Your answer:
—
·
Correct:
C
Explanation
The outbound speed is 40 km/h and the return speed is 50% higher, i.e., 60 km/h. For a round trip with equal distances each way, the average speed is the harmonic mean: 2ab/(a+b). Substituting a = 40 and b = 60 gives (2×40×60)/(40+60) = 4800/100 = 48 km/h. Equivalently, for distance D each way, times are D/40 and D/60, so total time = D(1/40+1/60)=D/24 and average speed = total distance/total time = 2D/(D/24) = 48 km/h, confirming the result. Therefore the correct choice is option 3 (48 kmph).
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