Lucas sits beside his friend Ben. Their teacher writes sums on the board. Lucas is ready to try the first one. The teacher asks him to come forward. He picks up a pen and looks at the sum. Then he writes his answer on the board. “That is right!” says the teacher. Lucas smiles and sits beside Ben. But Ben looks down at his book. “I do not know how to do this one.” Lucas moves his chair closer to Ben. “Let us work it out together.” He draws ten circles on some paper. Then he crosses out three of them. “How many circles are left?” he asks. Ben counts them and answers, “Seven!” He tries the next sum on his own. This time, Ben gets the answer right.