A batch of children's clothing costs 40 yuan each, and sells for 100 yuan. When half of this batch of clothing is sold, not only the cost is recovered, but also the profit is 600 yuan. How many pieces of this batch of children's clothing are there?
一批儿童服装，每件成本40元，销售100元，这批服装卖出一半时，不仅收回成本，而且盈利600元，这批童装共有多少件？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">100 * (1/2)</gadget>
<output>50</output>

<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<gadget id="calculator">600 / 10</gadget>
<output>60</output>

<result>60</result>