A man covers 2/3 of a journey at 40 km/h, 1/4 of the journey at 30 km/h and the remainder at 10 km/h. What is his average speed for the entire journey? MCQ with Answer and Explanation
A man covers 2/3 of a journey at 40 km/h, 1/4 of the journey at 30 km/h and the remainder at 10 km/h. What is his average speed for the entire journey?
A. 36 km/h
B. 30 km/h
C. 25 km/h
D. 32 km/h
Answer: Option D
Solution (By JKSSB Mock Tests)
Let the total distance be 120 km. First part = (2/3) * 120 = 80 km; Time = 80 / 40 = 2 hours. Second part = (1/4) * 120 = 30 km; Time = 30 / 30 = 1 hour. Remainder = 120 - 80 - 30 = 10 km; Time = 10 / 10 = 1 hour. Total time = 2 + 1 + 1 = 4 hours. Average speed = 120 / 4 = 32 km/h.
A motorboat covers a certain distance downstream in 4 hours and covers the same distance upstream in 5 hours. If the speed of the stream is 2 km/h, find the speed of the motorboat in still water.
Explanation:
Let speed of boat in still water be v. Downstream speed = v + 2, Upstream speed = v - 4. Distance is same, so 4(v + 2) = 5(v - 2) => 4v + 8 = 5v - 10 => v = 18 km/h.
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