First make 3/5 into a percent or whole number because it's easier to solve that way. How do you do that? Divide it how it is, so 3/5 = 0.60. So 60% of her class has at least one pet.
Knowing this, we multiply 60% by 20 to know how many students are that 60% that have pets. So 0.6 x 20= 12
