The volume of a fish tank is 30 cubic feet. If the density is 0.3fish over feet cubed, how many fish are in the tank?

The answer is 9 fish

The density (d) is the number of units (n) per volume (V):

d = n/V

We know:

d = 0.3 fish/ft³

V = 30 ft³

n = ?

d = n/V

n = d * V

n = 0.3 fish/ft³ * 30 ft³

n = 9 fish