A driver covers 30% of his total route at 30 km/h and the remaining 70% at 42 km/h. What is his average speed for the full trip? MCQ with Answer and Explanation
A driver covers 30% of his total route at 30 km/h and the remaining 70% at 42 km/h. What is his average speed for the full trip?
A. 40 km/h
B. 36 km/h
C. 38 km/h
D. 37.5 km/h
Answer: Option D
Solution (By JKSSB Mock Tests)
Let total distance be 100 km. First section = 30 km; Time = 30 / 30 = 1 hour. Second section = 70 km; Time = 70 / 42 = 5/3 hours. Total time = 1 + 5/3 = 8/3 hours. Average speed = 100 / (8/3) = 300 / 8 = 37.5 km/h.
A runner tracks a circular field loop course of radius 70 meters. If his speed registers at 20 m/s, find the total loop rounds completed by him in 2 minutes 12 seconds.
A boat goes 24 km upstream and 28 km downstream in 6 hours. It goes 30 km upstream and 21 km downstream in 6 hours 30 minutes. Find the speed of the boat in still water.
Explanation:
Let 1/u = x and 1/d = y. 24x + 28y = 6 and 30x + 21y = 6.5. Solving these linear equations gives x = 1/6 and y = 1/14. So upstream speed u = 6 km/h, downstream speed d = 14 km/h. Speed in still water = (d + u)/2 = (14 + 6)/2 = 10 km/h.
Two trains 140 meters and 160 meters long are tracking on parallel routes in opposite directions at 40 km/h and 50 km/h respectively. How long do they take to clear each other?
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