A bookstore has 10 Chinese, Mathematics, and English workbooks for different grades. How many ways are there to buy two of them?
某书店有不同年级的语文、数学、英语练习册各10本，买其中两本有多少种方法？
<gadget id="calculator">3 * 10 * 10</gadget>
<output>300</output>

<result>300</result>