Aquarium 1 will hold 5 small fish for every 10 gallons of water. If there are 200 gallons in the tank, you can sent up a proportion:
5 small fish/10 gallons = x small fish/ 200 gallons
if you cross multiply, you get
10x = 200 × 5
10x = 1000
x = 100
100 small fish will be in 200 gallons of water.
Aquarium 2 will hold 8 large fish for every 40 gallons of water. A proportion can also be set up here:
8 large fish/ 40 gallons = x large fish/ 200 gallons
if you cross multiply, you get:
40x = 200 × 8
40x = 1600
x = 40
40 large fish will be in 200 gallons of water.
the ratio of small fish to large fish:
100 small fish: 40 large fish
(both are divisible for 10, and if you divide both of them by ten you get)
10 small fish: 4 large fish
you can reduce again, since both are divisble by 2
5 small fish: 2 large fish
