Multiple choice

A car covers $\frac{2}{5}$ th of a distance at a speed of 80 km/h and $\frac{3}{5}$ th of the distance at a speed of 60 km/h. Average speed of car for complete journey is

  1. 65 km/h

  2. 70.5 km/h

  3. 66.67 km/h

  4. 77.5 km/h
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Average speed = Total distance / Total time. Let distance be D. Time = (2/5)D / 80 + (3/5)D / 60 = D/200 + D/100 = 3D/200. Average speed = D / (3D/200) = 200/3 = 66.67 km/h.

AI explanation

Assume the total distance is 5 km so the individual parts are 2 km and 3 km. The time taken for the first part is 2 divided by 80 hours, which is 1 divided by 40 hours, and the time taken for the second part is 3 divided by 60 hours, which is 1 divided by 20 hours. The total time is 3 divided by 40 hours, making the average speed the total distance of 5 km divided by (3 divided by 40) hours. This yields 200 divided by 3, which equals 66.67 km/h.

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