batch of science and technology books sold 640 copies on the first day, and sold the first day (7/8) on the second day. How many copies were sold on the second day?
一批科技书，第一天卖出640本，第二天卖出的是第一天的(7/8)，第二天卖出多少本？
<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">640 * (7/8)</gadget>
<output>560</output>

<result>560</result>