One pipe can fill a tank four times as fast as another pipe. If together the…
2025
One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in:
- A.
180 min
- B.
144 min
- C.
126 min
- D.
114 min
Attempted by 37 students.
Show answer & explanation
Correct answer: A
Solution:
Let the slower pipe take x minutes to fill the tank. Then the faster pipe, being four times as fast, takes x/4 minutes.
Their combined rate (tanks per minute) is 1/x + 1/(x/4) = 1/x + 4/x = 5/x.
They fill the tank together in 36 minutes, so the combined rate is 1/36. Set 5/x = 1/36 and solve for x.
Solve: x = 5 × 36 = 180. Therefore the slower pipe alone fills the tank in 180 minutes.
Check: rates are 1/180 and 1/45; together 1/180 + 1/45 = 5/180 = 1/36, so they take 36 minutes together, as given.