Wang Hong really wants to buy a book "Mathematics Olympiad Lectures" which costs 9.80 yuan. She adds 4.20 yuan to her existing money, and she just buys one. But she only bought a math competition book for 3.20 yuan, how much money does he have left?
王红很想买一本价格为9.80元的《数学奥林匹克讲座》书，她现有的钱再添4.20元，正好买一本．但是她只买了一本3.20元的数学竞赛书，他还剩下多少元钱？
<gadget id="calculator">9.8 - 4.2 - 3.2</gadget>
<output>2.4</output>

<result>2.4</result>