Li Ming bought two books in the bookstore. One copy is 19.5 yuan, and the other is 21.8 yuan. He pays 50 yuan, how much should he get back?
李明在书店买了两本书．一本19.5元，另一本21.8元．他付出50元，应找回多少元？
<gadget id="calculator">50 - 19.5 - 21.8</gadget>
<output>8.7</output>

<result>8.7</result>