George has 3 small pizzas * 4 slices = <<3*4=12>>12 pieces.
George also has 2 large pizzas * 8 slices = <<2*8=16>>16 slices.
Total, George has 12 + 16 slices = <<12+16=28>>28 slices of pizza.
Bob will eat 3 slices + 1 = <<3+1=4>>4 slices.
Susie will eat 1/2 * 4 slices = <<1/2*4=2>>2 slices.
Bob, Fred and Mark will eat in total 3 + 3 + 3 = <<3+3+3=9>>9 pieces.
Total slices of pizza eaten will be 3 + 4 + 2 + 9 = <<3+4+2+9=18>>18 pieces.
Total pizza slices remaining will be 28 pieces - 18 = <<28-18=10>>10 slices left.
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