The teacher thought of a number in his mind, and said to his students: "Add 9 to this number, and then take half of the sum to be 5," then what is the number.
老师心中想一个数，对他的学生说："给这个数加上9，再取和的一半是5，"则这个数是多少．
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 9</gadget>
<output>1</output>

<result>1</result>