Red Star Supermarket shipped 1,000 exercise books, and after 15 days of selling, there are 40 left. How many copies are sold per day on average?
红星超市运来1000本练习本，卖了15天后，还剩40本，平均每天卖出多少本？
<gadget id="calculator">1_000 - 40</gadget>
<output>960</output>

<gadget id="calculator">960 / 15</gadget>
<output>64</output>

<result>64</result>