you need 2 eggs to make 20 cookies. Find out how much cookies one egg makes.
20/2 = 10
1 egg = 10 cookies
now multiply 10 to both sides to find out how much eggs are needed for 100 cookies
1 egg (10) = 10 cookies (10)
1(10) = 10(10)
10 = 100
You need 10 eggs to make 100 cookies
hope this helps