There are 18 animals. Some cows and some ducks with a total of 60 legs. How many cows and how many ducks?

X + Y = 18

X=chickens, Y=Cows

2x + 4y = 60

Let's try 8 and 10.

16 + 40=56, no, 32+20=52, no. 8&10 do not work.

Let's try 9 and 9.

18+36=54, no. 9&9 do not work.

Let's try 11 & 7.

22+28=50, no. 14+44=58, no.

Let's try 12 & 6.

24+24=48, no. 12+48=60 YES!

There are 12 cows and 6 chickens.