An animal shelter spends $2.50 per day to care for each bird and $7.50 per day to care for each cat. Allison noticed that the shelter spent $62.50 caring for birds and cats on Monday. Allison found a record showing that there were a total of 19 birds and cats on Monday. How many birds were at the shelter on Monday?

Answer = 16 birds

1. Write out your equations
X = birds
Y= cats
x + y = 19
2.50x + 7.50y = 62.50

2. Isolate one variable.
x + y = 19
x = 19 - y

3. Plug this in as the variable in the other equation. Then, solve.
2.5(19 - y) + 7.5y = 62.5
47.5 - 2.5y + 7.5y = 62.5
-2.5y + 7.5y = 15
5y = 15
y = 3 (cats)

4. Solve for the other variable.
We know there were 19 animals in total on Monday. Since there were 3 cats, there must be 16 birds.

5. Double check by plugging the numbers into the original equations.
16 + 3 = 19
19 = 19 (true)

2.5(16) + 7.5(3) = 62.5
40 + 22.5 = 62.5
62.5 = 62.5 (true)