The store buys a batch of pens at a price of 10 yuan each, and then sells them at a fixed price after adding 40% of the profit. When (2/4) of this batch of pens is sold, the profit is already 240 yuan. How many pens are there in this batch ?
商店以每支10元的价格购进一批钢笔，加上40%的利润以后定价出售，当卖出这批钢笔的(2/4)时就已经获利240元，这批钢笔共有多少支？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">10 * (2/5)</gadget>
<output>4</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">240 / 4 / (1/2)</gadget>
<output>120</output>

<result>120</result>