Obviously reading a storybook, he has already read 30 pages. At this time, he finds that the ratio of the number of pages he has read to the number of unread pages is 2:5. How many pages does this storybook have?
明明读一本故事书，已经读了30页，这时他发现已读的页数和未读的页数的比是2：5，这本故事书共有多少页？
<gadget id="calculator">2 + 7</gadget>
<output>9</output>

<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">30 / (2/9)</gadget>
<output>135</output>

<result>135</result>