Zhang Hua reads a story book. On the first day, he reads 1/3 of the whole book, and on the second day, he reads 20 pages. At this time, he just read half of the whole book. How many pages are left?
张华看一本故事书，第一天看了全书的(1/3)，第二天看了20页，这时正好看了全书的一半，还剩多少页没看？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/2) - (1/3)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">20 / (1/6)</gadget>
<output>120</output>

<gadget id="calculator">120 * (1/2)</gadget>
<output>60</output>

<result>60</result>