jean stocked her aquarium with 36 fresh-water fish, which cost $212. the male fish cost $5 each, while the female fish cost $7 each. find the number of male fish (x) and the number of female fish (y)

Let x = number of male fish

Let y = number of female fish.

We need to construct a system of equations to solve this problem.

36 = x + y

212 = 5x + 7y. Lets solve this by elimination. Multiply the first equation by - 5

-180 = - 5x + - 5y

212 = 5x + 7y. Now we need to add the equations together.

32 = 2y. Divide each side by 2.

16 = y. Plug this number into one of our original equations.

36 = x + (16). Subtract 16 from both sides.

20 = x.

There are 20 male fish and 16 female fish.