A batch of books has been repaired, and 50 books have been repaired, which is 25% of the number of unrepaired books. How many books are there in this batch?
修补一批图书，已经修补了50本，是未修补本数的25%，这批图书一共有多少本？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">50 / (1/4)</gadget>
<output>200</output>

<gadget id="calculator">200 + 50</gadget>
<output>250</output>

<result>250</result>