Use a batch of paper to bind exercise books of the same size. If each book has 30 pages, there will be 20 more papers; if each book has 40 pages, there will be 2 fewer books. How many sheets are there in total? (solution with equation)
用一批纸装订同样大小的练习本，如果每本30页则多出20张纸；如果每本40页则少2本．这批纸一共多少张？(用方程解答)
<gadget id="calculator">20 / 30</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(2/3) + 2</gadget>
<output>8/3 = around 2.666667</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/30) - (1/40)</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">(8/3) / (1/120)</gadget>
<output>320</output>

<result>320</result>