20 yellow balls, 15 white balls, and 5 red balls are mixed in a box. If one is picked at random, what is the probability of catching a white ball?
20个黄球、15个白球、5个红球混装在盒中，任意抓取一个，抓到白球的可能性大小是多少．
<gadget id="calculator">20 + 15 + 5</gadget>
<output>40</output>

<gadget id="calculator">15 / 40</gadget>
<output>3/8 = around 0.375</output>

<result>3/8 = around 0.375</result>