A stack of 33 CDs is 1.5 inches high.

How many CDs would be in a stack that is 3.5 inches high?

33 CDs is 1.5 inches, so by dividing by 3, you learn that 11 CDs is .5 inches.

33=1.5
33÷3=1.5÷3
11=.5
11(7)=.5(7)
77=3.5

So 77 CDs is 3.5 inches