When we add we count up. We have $\displaystyle 1$ triangle in the first box, and then $\displaystyle 9$ triangles in the second box. In total we have $\displaystyle 10$ triangles. If you start at $\displaystyle 1$ on a number line and count up $\displaystyle 9$, you have $\displaystyle 10$.

$\displaystyle 1, 2,3,4,5,6,7,8,9,10$

When we add we count up. We have $\displaystyle 1$ triangle in the first box, and then $\displaystyle 0$ triangles in the second box. In total we have $\displaystyle 1$ triangle. If you start at $\displaystyle 1$ on a number line and count up $\displaystyle 0$, you are still at $\displaystyle 1$.

$\displaystyle 1$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 1$ triangle in the second box. In total we have $\displaystyle 3$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 1$, you have $\displaystyle 3$.

$\displaystyle 2,3$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 0$ triangles in the second box. In total we have $\displaystyle 2$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 0$, you still have $\displaystyle 2$.

$\displaystyle 2$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 2$ triangles in the second box. In total we have $\displaystyle 4$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 2$, you have $\displaystyle 4$.

$\displaystyle 2,3,4$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 3$ triangles in the second box. In total we have $\displaystyle 5$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 3$, you have $\displaystyle 5$.

$\displaystyle 2,3,4,5$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 4$ triangles in the second box. In total we have $\displaystyle 6$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 4$, you have $\displaystyle 6$.

$\displaystyle 2,3,4,5,6$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 5$ triangles in the second box. In total we have $\displaystyle 7$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 5$, you have $\displaystyle 7$.

$\displaystyle 2,3,4,5,6,7$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 6$ triangles in the second box. In total we have $\displaystyle 7$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 6$, you have $\displaystyle 8$.

$\displaystyle 2,3,4,5,6,7,8$

When we add we count up. We have $\displaystyle 2$ triangles in the first box, and then $\displaystyle 7$ triangles in the second box. In total we have $\displaystyle 9$ triangles. If you start at $\displaystyle 2$ on a number line and count up $\displaystyle 7$, you have $\displaystyle 9$.

$\displaystyle 2,3,4,5,6,7,8,9$