Teacher Wang wants to buy 24 copies of "Stories of Idioms" for the class, and the public bookstore stipulates that they will be sold at a discount of 10% from the original price. Qiuzhi Bookstore stipulates: buy 5 books and get 1 free. Less than 5 copies will not be given away. The price of "Story of Idioms" in two bookstores is 10 yuan. May I ask which bookstore is cheaper for Mr. Wang? How much is the minimum cost?
王老师要为班级买24本《成语故事》，大众书店规定：按原价优惠10%销售．求知书店规定：每买5本赠送1本．不满5本不赠送．两个书店的《成语故事》标价都是10元，请问王老师到哪个书店比较便宜？最少花多少元？
<gadget id="calculator">24 / 6</gadget>
<output>4</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<result>200</result>