Mr. Li bought three books with prices of 6.80 yuan, 5.75 yuan and 6.20 yuan respectively. He paid 20 yuan, how much should he get back?
李老师买了三本书，价格分别是6.80元、5.75元、6.20元，他付出20元钱，应找回多少钱？
<gadget id="calculator">6.8 + 5.75 + 6.2</gadget>
<output>18.75</output>

<gadget id="calculator">20 - 18.75</gadget>
<output>1.25</output>

<result>1.25</result>