There are 5 red balls and 4 yellow balls in a wooden box, which are identical except for their color. Now draw a ball from it, what is the probability that it is a red ball?
木箱里有5个红球和4个黄球，它们除颜色外完全相同．现在从中摸出1个球，是红色球的可能性是多少．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<result>5/9 = around 0.555556</result>