On Sunday, Xiaolan took the 50 yuan her mother gave her to the bookstore to buy books. He first bought 7 "Story Books" with the same price for 30.8 yuan, and planned to use the remaining money to buy "One Hundred Thousand Whys" at 9.6 yuan each. How many copies of "One Hundred Thousand Whys" can Xiaolan buy?
星期天，小兰带上妈妈给的50元钱去买书店买书．他先花30.8元买了7本价格相同的《故事书》，并准备用剩下的钱买《十万个为什么》，每本9.6元．请问小兰还可以买几本《十万个为什么》？
<gadget id="calculator">50 - 30.8</gadget>
<output>19.2</output>

<gadget id="calculator">19.2 / 9.6</gadget>
<output>2</output>

<result>2</result>