The stationery store buys 310 boxes of crayons, and the number of boxes of watercolor pens is twice that of crayons. How many more boxes of watercolor pencils than crayons do stationery stores buy?
文具店购进蜡笔310盒，水彩笔的盒数是蜡笔的2倍．文具店购进的水彩笔比蜡笔多多少盒？
<gadget id="calculator">310 * 2</gadget>
<output>620</output>

<gadget id="calculator">620 - 310</gadget>
<output>310</output>

<result>310</result>