given:
fill 5L tank using 250 ml container .
to find:
how many full containers are required to fill the tank.
solution:
1 L= 1000 mL
1000 mL/250mL = 4
1 L= 4 full containers
4 containers x 5 liters = 20 full containers.
so, 20 full containers are required to fill the fish tank.