For a book, I read (1/5) of the whole book on the first day, and 12 pages on the second day. At this time, there is still (1/2) of the whole book left. How many pages did I read on the first day?
一本书，第一天看了全书的(1/5)，第二天看了12页，这时还剩全书的(1/2)，第一天看了多少页？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/5) - (1/2)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">12 / (3/10)</gadget>
<output>40</output>

<gadget id="calculator">40 * (1/5)</gadget>
<output>8</output>

<result>8</result>