Xiao Ming reads a book. He reads 30 pages on the first day and 40 pages on the second day. At this time, the ratio of the number of pages he has read to the number of pages he has not read is 2:5. How many pages are there in this book?
小明看一本书，第一天看了30页，第二天看了40页，这时已看的页数和未看的页数的比是2：5，这本书共有多少页？
<gadget id="calculator">30 + 40</gadget>
<output>70</output>

<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">70 / (2/7)</gadget>
<output>245</output>

<result>245</result>