There are 1 red ball, 1 green ball, and 2 white balls in a box, all of which are the same except for their color. If two balls are randomly drawn from the box at a time, what is the probability that both balls are white?
一个盒子里有1个红球，1个绿球，2个白球，除颜色外其余都相同，现随机从盒子里一次取出两个球，则这两个球都是白球的可能性是多少
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<result>1/6 = around 0.166667</result>