The school purchased 720 science and technology books at the Beijing Book Market, 180 more than twice the number of story books. How many story books did the school buy? (Solution by two methods of arithmetic and equation)
学校在北京书市购得科技书720本，比故事书的2倍多180本，学校买故事书多少本？(用算术、方程两种方法解)
<gadget id="calculator">720 - 180</gadget>
<output>540</output>

<gadget id="calculator">540 / 2</gadget>
<output>270</output>

<result>270</result>