Naughty bought a book for 6.5 yuan and bought a pen for 11.3 yuan. He paid the salesperson 20 yuan. How much should he get back?
淘气买一本书用去6.5元，买一支钢笔用去11.3元，他付给售货员20元，应找回多少元？
<gadget id="calculator">6.5 + 11.3</gadget>
<output>17.8</output>

<gadget id="calculator">20 - 17.8</gadget>
<output>2.2</output>

<result>2.2</result>