A book has 80 pages in total. I read (1/4) of it for the first time, and the rest (2/3) for the second time. How many pages are left?
一本书共80页，第一次看了它的(1/4)，第二次看了余下的(2/3)，还有多少页没有看？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(3/4) * (2/3)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/4) - (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">80 * (1/4)</gadget>
<output>20</output>

<result>20</result>