Xiao Ming has 20 yuan. He wants to buy a story book of 5.5 yuan and a pen of 15.80 yuan, how much is the difference?
小明有20元钱．他想买一本5.5元的故事书和一支15.80元的钢笔，还差多少元钱？
<gadget id="calculator">15.8 - 20</gadget>
<output>-4.2</output>

<gadget id="calculator">5.5 + (-4.2)</gadget>
<output>1.3</output>

<result>1.3</result>