When Xiaohua reads a book, the ratio of what he has already read to the total number of pages is 1:3, and if he reads 15 more pages, he will read the entire book (1/2). How many pages does this book have?
小华看一本书，已经看的与总页数的比是1：3，再看15页，则正好看完全书的(1/2)．这本书共有多少页？
<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">10 / (1/6)</gadget>
<output>60</output>

<result>60</result>