Multiple choice

A bus travelling the first one third distance at a speed of $10 km/h$, the next one third at$20 km/h$ and the last one third at $60 km/h$. The average speed of the bus is

  1. $9 km/h$
  2. $16 km/h$
  3. $18 km/h$
  4. $48 km/h$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Average speed = Total distance / Total time. Let total distance be 3d. Time = d/10 + d/20 + d/60 = (6d + 3d + d) / 60 = 10d/60 = d/6. Average speed = 3d / (d/6) = 18 km/h.

AI explanation

For a journey where equal distances are traveled at different speeds, the average speed is calculated using the formula 3abc divided by (ab + bc + ca). Substituting the speeds 10, 20, and 60 gives a numerator of 3 * 10 * 20 * 60 equaling 36000. The denominator is (10 * 20) + (20 * 60) + (60 * 10) equaling 2000, making the average speed 36000/2000, which is 18 km/h.