You are filling a 5-L fish tank using a 250-mL container. How many full containers are required to fill the fish tank?

To calculate how many full containers are required to fill the fish tank, you need to divide the total volume of the fish tank by the volume of the 250-mL container.

5 L = 5000 mL

Number of full containers = 5000 mL / 250 mL = 20

So, 20 full containers are required to fill the fish tank.