Teacher Li bought back 50 exercise books at 80 cents apiece and 40 cents apiece at a cost of RMB 32. How many exercise books are there for 8 jiao.
李老师买回8角钱一本的练习本和4角钱一本的练习本共50本，付出人民币32元．8角一本的练习本有多少本．
<gadget id="calculator">50 * 0.4</gadget>
<output>20</output>

<gadget id="calculator">32 - 20</gadget>
<output>12</output>

<gadget id="calculator">0.8 - 0.4</gadget>
<output>0.4</output>

<gadget id="calculator">12 / 0.4</gadget>
<output>30</output>

<result>30</result>