G2.1 一個盒子有五個球, 球面上分別印上號碼 3、4、6、9 或 10 。由盒中同時隨機取出 2 個球, 並得出其號碼的總和。若 $A$ 為不同總和的數量, 求 $A$ 的值。
A box contains five distinctly marked balls with number markings being $3,4,6,9$ or 10 . Two balls are randomly drawn without replacement from the box. If $A$ is the number of possible distinct sums of the selected numbers, determine the value of $A$.
$$
\begin{array}{l}
3+4=7,3+6=9,3+9=12,3+10=13,4+6=10,4+9=13,4+10=14,6+9=15 \\
6+10=16,9+10=19
\end{array}
$$

The distinct sums are $7,9,10,12,13,14,15,16,19 . A=9$