One pump can empty a pool in 7 days, whereas a second pump can empty the pool in 13 days. How long will it take the two pumps, working together, to empty the pool? (Fractional answers are OK)
1. The first pump's rate is _______ per day.
2. The second pump's rate is _______ per day.
3. The combined pumps rate is _______ per day.
4. It will take the two pumps _______ days to empty the pool together.