Mom spent 15.8 yuan on pens and 24.4 yuan on books. Pay 50 yuan to the salesperson's aunt, how much should I get back?
妈妈买钢笔花了15.8元，买书花了24.4元．付给售货员阿姨50元，应找回多少元？
<gadget id="calculator">15.8 + 24.4</gadget>
<output>40.2</output>

<gadget id="calculator">50 - 40.2</gadget>
<output>9.8</output>

<result>9.8</result>