The school bought a batch of exercise books and distributed them to three classes. Class A was assigned 40%, Class B was assigned 5:7, and Class C was assigned 20 more books than Class B. How many exercise books are there in this batch?
学校买来一批练习本分给三个班，甲班分到40%，乙班分到的与甲班的比是5：7，丙班比乙班多分到20本．这批练习本有多少本？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(2/5) * (5/7)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/5) - (2/7) - (2/7)</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">20 / (1/35)</gadget>
<output>700</output>

<result>700</result>