An automobile travels from city A to city B and returns to city A by the same route. The speed of the vehicle during the onward and return journeys were constant at 60 km/h and 90 km/h, respectively. What is the average speed in km/h for the entire journey?
Options:
(A) 72
(B) 73
(C) 74
(D) 75
Official Answer Key:
A
Step-by-Step Solution & Explanation
Equal distances ⇒ average speed is the harmonic mean of the two speeds.
V_avg = 2v₁v₂/(v₁+v₂) = 2 × 60 × 90 / (60+90) = 10800/150 = 72 km/h.
Distractor (D) 75 is the arithmetic mean (60+90)/2 — the classic error, valid only for equal times, not equal distances.
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.