There are a number of red and green balls in the box, among which there are 42 red balls, accounting for 60% of the total, and after how many green balls are put in, the green balls account for 50% of the original total.
盒子中有红、绿两种颜色的球若干个，其中红球有42个，占总数60%，再放入多少个绿球后，绿球占原来总数的50%．
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">42 / (3/5)</gadget>
<output>70</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">70 * (1/10)</gadget>
<output>7</output>

<result>7</result>