Additionner à l'aide d'une demi-droite graduée

A number line with 3 unequally spaced tick marks. From left to right, the tick marks are labeled 480, an unlabeled tick mark, and an unlabeled tick mark. An arrow labeled plus 20 is above the number line beginning at 480 and ending at the first unlabeled point. An arrow labeled plus 139 is above the number line beginning at the first unlabeled point and ending at the second unlabeled point. An arrow labeled plus 159 is above the number line beginning at 480 and ending at the second unlabeled point.