There are only 3 red balls in the pocket, and one is randomly touched, so that the possibility of drawing a red ball is (1/5), how many balls of other colors must be put in the pocket. (the shape, size and weight of the balls are all the same)
口袋里只有3个红球，任意摸1个，要使摸出红球的可能性为(1/5)，还要往口袋里放多少个其它颜色的球．(球的形状、大小、重量均相同)
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / (1/5)</gadget>
<output>15</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>