After A ate ¼, that would leave ¾ for B, who took ⅓, that is, ¼ of the original pizza. So A and B each took a quarter, so together they took half, which was left for C. To make it easier, cut the pizza into 4 pieces of the same size. So A takes 1 piece, leaving 3 pieces. B takes a third, which is one piece. That leaves 2 pieces for C, which is half the pizza.
