The stationery store bought a batch of exercise books at the wholesale price of 0.35 yuan each, and the retail price of 0.4 yuan each. When the remaining 200 exercise books were sold, all the costs had been recovered and a profit of 10 yuan was made. How many exercise books does the store buy?
文化用品商店按批发价买进一批练习本，每本0.35元，零售价每本0.4元，当卖到剩下200本练习本时，已经收回了全部成本，还获利10元．商店买进练习本多少本？
<gadget id="calculator">200 * 0.4</gadget>
<output>80</output>

<gadget id="calculator">10 + 80</gadget>
<output>90</output>

<gadget id="calculator">0.4 - 0.35</gadget>
<output>0.05</output>

<gadget id="calculator">90 / 0.05</gadget>
<output>1_800</output>

<result>1_800</result>