In the center of the library is a fountain that holds 500 gallons of water. For every 25 gallons of water they must add 1/4 cup of water treatment. How many cups of water treatment must they add to the fountain to treat the 500 gallons of water?

(500/25) * 1/4 = ?

To find out how many cups of water treatment they need to add to the fountain, we first need to determine the number of 25-gallon increments present in 500 gallons of water.

We can do this by dividing the total gallons of water (500) by the quantity of water in each increment (25):

500 gallons ÷ 25 gallons = 20 increments

Next, we need to calculate the number of cups of water treatment required for each increment. According to the given information, 1/4 cup of water treatment is needed for every 25 gallons of water.

Therefore, for each 25-gallon increment, they need to add 1/4 cup of water treatment.

Finally, we multiply the number of increments by the amount of water treatment needed for each increment:

20 increments × 1/4 cup = 5 cups

Therefore, they need to add 5 cups of water treatment to treat the 500 gallons of water in the fountain.