A car covers the first 12 km distance at a speed of 30 km per hour, the next 15 km distance at a speed of 45 km/h, and the next 20 km distance at a speed of 60 km/h. Find the average speed of the car.
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3, i.e., km/h.
Average speed = Total distance ÷ Total time
Total distance = 12 + 15 + 20 = 47 km
Time for first part = 12 ÷ 30 = 2/5 h
Time for second part = 15 ÷ 45 = 1/3 h
Time for third part = 20 ÷ 60 = 1/3 h
Total time = 2/5 + 1/3 + 1/3 = 2/5 + 2/3 = (6 + 10) ÷ 15 = 16/15 h
Average speed = 47 ÷ (16/15) = 47 × 15 ÷ 16 = 705 ÷ 16 = km/h