The school purchased a batch of story books and technology books, a total of 480, of which story books accounted for (3/10) of the total, and later bought some story books, and at this time technology books accounted for the total (21/50). How many storybooks did you buy?
学校购进一批故事书和科技书，共480本，其中故事书占总数的(3/10)，后来又购买了一些故事书，这时科技书占总数的(21/50)，学校后来购买了多少本故事书？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">480 * (3/10)</gadget>
<output>144</output>

<gadget id="calculator">480 - 144</gadget>
<output>336</output>

<gadget id="calculator">21 / 50</gadget>
<output>21/50 = around 0.42</output>

<gadget id="calculator">336 / (21/50)</gadget>
<output>800</output>

<gadget id="calculator">800 - 480</gadget>
<output>320</output>

<result>320</result>