Answer:
25 gallons.
Explanation:
The container that holds the water for the football team is 1/2 full.
After pouring out 5 gallons of water, it is 3/10 full.
The proportion that was poured out is 
 -
 - 
 =
 = 
 =
 = 

 of the water in the container is equal to 5 gallons
 of the water in the container is equal to 5 gallons
The container therefore holds: 1 × 5 ÷ 
 = 5 × 5 = 25 gallons.
 = 5 × 5 = 25 gallons.