Use a batch of paper to bind exercise books of the same size. If each book is bound with 30 pages, 280 books can be bound. If each exercise book is bound with 10 more pages, how many exercise books can this batch of paper hold. (Answer with proportional knowledge)
用一批纸装订同样大小的练习本，如果每本装订30页，能装订280本，如果每本练习本多装订10页，这批纸只能装多少本练习本．(用比例知识解答)
<gadget id="calculator">30 * 280</gadget>
<output>8_400</output>

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

<gadget id="calculator">8_400 / 40</gadget>
<output>210</output>

<result>210</result>