A large water tank can be filled by a pump A in 10 minutes, and by B can fill…
2023
A large water tank can be filled by a pump A in 10 minutes, and by B can fill the same tank in 20 minutes. If both the pumps work together to fill the tank, how long will it take to fill the tank.
- A.
1 hrs 10 minutes
- B.
20/3 minutes
- C.
4 minutes
- D.
20/9 minutes
Attempted by 40 students.
Show answer & explanation
Correct answer: B
Solution:
Find each pump's rate in tanks per minute: pump A fills the tank in 10 minutes, so its rate is 1/10 tank per minute. Pump B fills the tank in 20 minutes, so its rate is 1/20 tank per minute.
Add the rates to get the combined rate: 1/10 + 1/20 = 2/20 + 1/20 = 3/20 tank per minute.
Time to fill one whole tank = 1 ÷ (combined rate) = 1 ÷ (3/20) = 20/3 minutes.
Convert 20/3 minutes to minutes and seconds: 20/3 = 6 and 2/3 minutes; 2/3 minute = 40 seconds. So the time is 6 minutes 40 seconds.
Answer: 20/3 minutes (6 minutes 40 seconds).