The bookstore shipped 560 volumes of "Science Fiction Stories", and sold (2/7) of the total on the first day. How many volumes are still unsold?
书店运来《科幻故事》书560册，第一天卖出总数的(2/7)，这时还剩多少册未卖出？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">560 * (2/7)</gadget>
<output>160</output>

<gadget id="calculator">560 - 160</gadget>
<output>400</output>

<result>400</result>