For a book, the ratio of the number of pages read to the number of remaining pages is 2:3, how much has been read in this book.
一本书，读过的页数与剩余页数的比是2：3，这本书已读了多少．
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>