An air conditioner can cool the hall in 40 minutes, while another takes 45…
2023
An air conditioner can cool the hall in 40 minutes, while another takes 45 minutes to cool under similar conditions. If both air conditioners are switched on at the same time, how long will it take to cool the room?
- A.
About 22 minutes
- B.
About 20 minutes
- C.
About 18 minutes
- D.
About 25 minutes
Attempted by 61 students.
Show answer & explanation
Correct answer: A
Solution: compute the combined cooling time.
Rate of first air conditioner = 1/40 room per minute; rate of second = 1/45 room per minute.
Combined rate = 1/40 + 1/45 = (9 + 8)/360 = 17/360 room per minute.
Time to cool one room = 1 / (combined rate) = 360/17 ≈ 21.176 minutes (≈ 21.18 minutes).
Among the choices given, "About 22 minutes" is the closest approximation to 21.18 minutes, so that option is the best answer.