A store buys a batch of table tennis rackets. The purchase price is 30 yuan per payment, and the retail price is 40 yuan per payment. When the remaining 100 payments are sold, the cost of purchasing this batch of rackets has been recovered. How many payments are there in total for this batch of rackets?
商店购进一批乒乓球拍，进价每付30元，零售价每付40元，当卖到还剩100付时，已收回购进这批球拍所用的成本，这批球拍共有多少付？
<gadget id="calculator">100 * 40</gadget>
<output>4_000</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<gadget id="calculator">4_000 / 10</gadget>
<output>400</output>

<result>400</result>