Final answer:
After 15 days, the tank will have 0.400 gallons of water.
Step-by-step explanation:
To find the amount of water in the tank after 15 days, we need to keep track of the amount added and drained each day. First, we start with an empty tank and add 0.910 of a gallon on the first day. This gives us a total of 0.910 gallons in the tank.
On the second day, we drain 0.710 of a gallon from the tank. This means we subtract 0.710 from the previous total, leaving us with 0.200 gallons in the tank.
On the third day, we add 0.810 of a gallon. Adding this to the previous total of 0.200 gallons gives us a new total of 1.010 gallons.
On the fourth day, we drain 0.610 of a gallon. Subtracting this from the previous total of 1.010 gallons gives us a new total of 0.400 gallons.
We can continue this pattern for the remaining days, adding and subtracting the given amounts. After completing the calculations for all 15 days, the final amount of water in the tank is 0.400 gallons.