Three-eighth of a journey is covered at a speed of 60 km/hr, and the remaining distance is covered at the rate of 40 km/hr. The average speed for the whole journey (in km/hr, rounded off to the nearest integer) is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 46
Let total distance = 1 unit
Distance 1 = 3/8, Distance 2 = 5/8
Time 1 = Distance ÷ Speed = (3/8) ÷ 60 = 3 ÷ (8 × 60) = 3/480 = 1/160 hours
Time 2 = (5/8) ÷ 40 = 5 ÷ (8 × 40) = 5/320 = 1/64 hours
Total time = 1/160 + 1/64 = (1 + 2.5)/160 = 3.5/160 = 7/320 hours
Average speed = Total distance ÷ Total time
= 1 ÷ (7/320) = 320/7 ≈ 45.71 ≈ 46 km/hr