A 12-inch pizza has double the diameter of the 6-inch pizza, so will have 2² = 4 times the area. 1/8 of that pizza will have 4/8 = 1/2 the area of the personal pizza. If calories are proportional to the area, then the slice will have ...
(1/2)(620 calories) = 310 calories . . . in 1 slice of 12-in pizza
