Question

A farmhouse shelters 20 animals. Some are cows, and some are ducks. Altogether there are 64 legs. How many cows are there?

Answer 1

Let c=cows and d=ducks

Create the following equations:

Total Animals. c + d = 20
Total Legs. 4c + 2d = 64

Using the first equation solve for d and substitute into the second equation and solve for c

d=20-c

4c + 2(20 - c) = 64
4c + 40 - 2c = 64
2c = 24
c=12

There were 12 cows