John and Sam were hungry so they ordered an extra-large pizza that was pre-sliced into 12 pieces.  John ate 3 slices while Sam ate twice the amount that John ate.  How many slices of pizza were left?
Sam had twice the amount of John so Sam ate 3*2 = <<3*2=6>>6 slices
Together, they ate 3+6 = <<3+6=9>>9 slices
1 pizza has 12 slices. 9 slices were eaten so 12-9= <<12-9=3>>3 slices left.
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