One-third of a journey is covered at a speed of 25 km/h, the next one-third of the journey is covered at a speed of 40 km/h and the remaining journey is covered at a speed of 50 km/h. The average speed (in km/h, rounded off to 1 decimal place) for the entire journey is:

Question

Question

This question was previously asked in

RRB Group D 13 Sept 2022 Shift 2 Official Paper

Answer 1

Given:

n = 3

S₁ = 25 km/h

S₂ = 40 km/h

S₃ = 50 km/h

Formula Used:

If a distance is divided in 'n' equal parts each travelled with different speeds, then

Average Speed = \(\frac{n}{\frac{1}{S_1}+\frac{1}{S_2}+\frac{1}{S_3}+....+\frac{1}{S_n}}\)

Where, n = Number of equal parts

Calculation:

Average Speed = \(\frac{3}{\frac{1}{25}+\frac{1}{40}+\frac{1}{50}}\)

⇒ Average Speed = \(\frac{3}{\frac{8}{200}+\frac{5}{200}+\frac{4}{200}}\)

⇒ Average Speed = 3 ÷ (17/200)

⇒ Average Speed = (3 × 200)/17 = 35.29 ≈ 35.3 km/h

∴ The average speed for the entire journey is 35.3 km/h.