Multiple choice

A car covers $4$ successive $3$ km stretches at speeds of $10$ km/hr, $20$ km/hr, $30$ km/hr and $60$ km/hr respectively. The average speed of the car for the entire journey is

  1. $15$ km/hr
  2. $35$ km/hr
  3. $20$ km/hr
  4. $25$ km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Average speed = Total distance / Total time. Total distance = 4 * 3 = 12 km. Total time = 3/10 + 3/20 + 3/30 + 3/60 = (18+9+6+3)/60 = 36/60 = 0.6 hours. Average speed = 12 / 0.6 = 20 km/hr.

AI explanation

The total distance is 4 stretches of 3 km each, giving 12 km. Using the formula time equals distance divided by speed, the times for the four stretches are 3/10, 3/20, 3/30 and 3/60 hours respectively, which sum to 3/5 hours. The average speed is 12 km divided by 3/5 hours, which equals 20 km/hr.

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