Multiple choice

In a journey of three unequal laps, a car covers a distance of 200 km in 4 h in the first lap, while another 162 km at the speed of 15 m/s in the second lap. It covered the remaining distance of the final lap in 4 h such that the average speed of the car for entire journey was 50 km/h. What was the speed of the car in the third lap of the journey?

  1. 47 km/h

  2. 52 km/h

  3. 42 km/h

  4. 45 km/h
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A Correct answer
Explanation

Lap 1: 200 km in 4h = 50 km/h. Lap 2: 162 km at 15 m/s = 54 km/h, time = 162/54 = 3h. Total average = 50 km/h. Total time needed = (total distance)/(avg speed) = (200 + 162 + d3)/50. Let t3 = 4h. Then (362 + d3)/50 = 4 + 3 + 4 = 11h, so d3 = 550 - 362 = 188 km. Speed in lap 3 = 188/4 = 47 km/h. Options B (52), C (42), and D (45) are incorrect.

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