while walking by a farmyard filled with chickens and rabbits, a farmer decided to count the heads and feet of his animals. He came up with a sum of 100 (counting both heads and feet). How many of each animal were in the farmyard?

Solution:

There are x chickens and y rabbits

So

2x+4y=100

x+y=30

So

x=10

y=20

So there 10 chickens and 20 rabbits