Xiaogang took 20 yuan to the store to buy a 7.5 yuan pencil case, so how much should the salesperson aunt give Xiaogang?
小刚带20元去商店买了一个7.5元的铅笔盒，那么售货员阿姨应该找多少元钱给小刚．
<gadget id="calculator">20 - 7.5</gadget>
<output>12.5</output>

<result>12.5</result>