Multiple choice

A pipes assembly can fill a cooling tank in 20 minutes, while a secondary drain outlet pipe can completely draw off the liquid volume in 30 min- utes. If both lines are activated concurrently from an empty state, how long will the system take to reach a full capacity state?

  1. 45 minutes

  2. 50 minutes

  3. 60 minutes

  4. 75 minutes

  5. none

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate of filling = 1/20. Rate of draining = 1/30. Net rate = 1/20 - 1/30 = (3-2)/60 = 1/60. Time to fill = 60 minutes.