Answer:
13.2 minutes or 13 minutes 12 seconds.
Step-by-step explanation:
1. Count how much water drains the first pump every minute. Let the volume of pool be D. Every minute first pump drains D/11 water.
2. Working together(6 minutes) First pump drains 6D/11 water, hence the second pump drains 5D/11 water.
3.Count how much water drains second pump per minute -> (5D/11)/6= 5D/66
4. It takes the second pump 66 minutes to drain pool 5 times, thus it takes 13.2(66/5) minutes to drain the pool, which is 13 minutes 12 seconds.