A police car starts chasing a fugitive in a BMW 3 hours after the BMW escapes…
2024
A police car starts chasing a fugitive in a BMW 3 hours after the BMW escapes from the scene of crime at 10 AM.The BMW drives for 10 km through the crowded roads of Shanghai and then drives into a highway, where the traffic allows vehicles to move twice as fast. After a while, the police car finally catches up with BMW after a chase that lasted 4 hours. By this time the moon was up in the sky for 4 hours. If the average speed of the police car is 83 kmph, then the average speed of the BMW (in kmph) is
Answer: D. 47.43 — Key idea: total distance covered by the police during the chase equals the total distance covered by the BMW when it was caught, so BMW average speed = that…
- A.
46.0
- B.
25.7
- C.
42.23
- D.
47.43
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Correct answer: D
Key idea: total distance covered by the police during the chase equals the total distance covered by the BMW when it was caught, so BMW average speed = that distance ÷ BMW's total travel time.
Distance covered by the police in the 4-hour chase = 4 × 83 = 332 km.
Total time the BMW was driving before being caught = 3 hours (lead time) + 4 hours (chase) = 7 hours.
Average speed of the BMW = total distance ÷ total time = 332 ÷ 7 ≈ 47.43 km/h.
Note: The intermediate detail that the BMW drove 10 km in crowded roads and then on a highway at twice that speed is not needed to compute the overall average speed once the total distance and total time are known.