A driver accounts 1/4 of his total delivery distance at 25 km/h and the remaining 3/4 at 75 km/h. Find his average speed for the full delivery route. MCQ with Answer and Explanation
A driver accounts 1/4 of his total delivery distance at 25 km/h and the remaining 3/4 at 75 km/h. Find his average speed for the full delivery route.
A. 50 km/h
B. 45 km/h
C. 60 km/h
D. 55 km/h
Answer: Option A
Solution (By JKSSB Mock Tests)
Let total distance be 100 km. First part = 25 km; Time = 24 / 25 = 1 hour. Remaining part = 75 km; Time = 75 / 75 = 1 hour. Total distance = 100 km, Total time = 2 hours. Average speed = 100 / 2 = 50 km/h.
Explanation:
Since time is inversely proportional to speed when distance is constant, the ratio of time taken is the reciprocal of the speed ratio: 1/3 : 1/5 = 5 : 3.
Explanation:
Time difference = 20 minutes = 20/60 = 1/3 hour. Let distance be d. d / 50 - d / 75 = 1/3 => (3d - 2d) / 150 = 1/3 => d / 150 = 1/3 => d = 50 km.
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