Put 1 red ball, 2 yellow balls, 3 black balls and 4 white balls in an opaque box. What is the probability of drawing a white ball?
在一个不透明的盒子里放入1个红球，2个黄球，3个黑球，4个白球．摸得白球的概率为多少．
<gadget id="calculator">1 + 2 + 3 + 4</gadget>
<output>10</output>

<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>