To find out how many pounds of turkey breast Joe will need for 20 people, he can set up a proportion and solve for x, the amount of turkey he needs.
pounds of turkey 5 x
# of people 8 = 20
Use cross products to solve for x.
8x = 5 x 20
8x = 100
8 8
x = 12.5 pounds
Joe will need 12.5 pounds of turkey.