You have exactly $100 to spend. You must get 100 animals. The chicks cost $0.50 each. The pigs cost $2.00 each. The sheep cost $5.00 each you must get some of each animals.

How many of each animals can you get.

c+p+s = 100

.5c + 2p + 5s = 100

There are lots of answers, as long as there are an even number of chicks (so you have whole dollars for their cost)

For example, getting the most sheep possible, you have
2 chicks, 4 pigs, 19 sheep
Now, you can start converting each pig into 4 chicks, down to
6 chicks, 3 pigs, 19 sheep
and so on to
186 chicks ,1 pig ,1 sheep