The school bought 206 science and technology books, 31 more than 2.5 times the number of story books. How many story books did it buy?
学校买来科技书206本，比故事书的2.5倍多31本，买来故事书多少本？
<gadget id="calculator">206 - 31</gadget>
<output>175</output>

<gadget id="calculator">175 / 2.5</gadget>
<output>70</output>

<result>70</result>