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Question : During a journey, a person travels half of the distance at a speed of 18 km/h and the remaining half of the journey at a speed of 22 km/h. What is his average speed for the entire journey?

Option 1: 21.4 km/h

Option 2: 20.2 km/h

Option 3: 19.2 km/h

Option 4: 19.8 km/h


Team Careers360 2nd Jan, 2024
Answer (1)
Team Careers360 13th Jan, 2024

Correct Answer: 19.8 km/h


Solution : Let $d$ be the total distance of the journey.
Half of the distance at 18 km/h and the remaining half at 22 km/h
⇒ Total Time for the journey = $\frac{d}{2×18}$ +$\frac{d}{2×22}$
⇒ average Speed = $\frac{\text{d}}{\text{​$\frac{d}{2×18}$ +$\frac{d}{2×22}$ }}$  = $\frac{\text{d}}{\text{​$\frac{22d}{2×18×22}$ +$\frac{18d}{2×18×22}$ }}$  = $\frac{d}{\frac{40d}{2×18×22}}$
= $\frac{18×22}{20}$
= 19.8
Hence, the correct answer is 19.8 km/h.

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