Put the same 4 yellow balls and 8 red balls in the bag, draw a ball at random, what is the probability that it is a yellow ball?
袋子时放同样的4个黄球和8个红球，任意摸出一个球，是黄球的可能性是多少．
<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">4 / 12</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>