A train travels at a speed of 18 m/s in the first 5 minutes, covers 7.5 km in the next 10 minutes and covers 12 km in another 10 minutes. What is its average speed (in km/h, rounded off to 1 decimal place) for the entire journey?

Question

Question

This question was previously asked in

SSC CGL 2022 Tier-I Official Paper (Held On : 13 Dec 2022 Shift 3)

Answer 1

Given:

Speed of train in the first 5 minutes (S₁)= 18 m/s

Distance travelled by train in the next 10 minutes (D₁)= 7.5 km

Distance travelled by train in the next 10 minutes (D₂)= 12 km

Formula used:

Average speed = Total distance/Total time taken

Distance = Speed × time

Calculation:

Distance travelled by train in the first 5 minutes = 18 × (5 × 60) = 5400 m = 5.4 km

Total time taken = (5/60) + (10/60) + (10/60)

⇒ (1/12) + (1/6) + (1/6) = (1 + 2 + 2)/12

⇒ 5/12

Average speed = Total distance/Total time taken

⇒ {(5.4 + 7.5 + 12) ×12}/5

⇒ {24.9 × 12}/5

⇒ 298.8/5 = 59.76 ≈ 59.8 km/h

∴ The correct answer is 59.8 km/h.

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