There are 12 people in the first group, 8 people like to eat watermelon, 10 people like to eat grapes, how many people like to eat both kinds of fruits.
第一小组有12人，喜欢吃西瓜的有8人，喜欢吃葡萄的有10人，两种水果都爱吃的有多少人．
<gadget id="calculator">10 - 12</gadget>
<output>-2</output>

<gadget id="calculator">8 + (-2)</gadget>
<output>6</output>

<result>6</result>