Water is added or drained from a tank each day. The first day, 910 of a gallon is added to the empty tank. The second day, 710 of a gallon is drained from the tank. The third day, 810 of a gallon is added to the tank. The fourth day, 610 of a gallon is drained from the tank. The amount of water in the tank after 15 days is given by 9/10+(−7/10)+8/10+(−6/10)+⋯+3/10+(− 1/10)+2/10.

How much water is in the tank after 15 days? Write your answer as a decimal.