There are 5 yellow balls and 4 red balls in a pocket. If you touch any one of them, what is the probability of getting a red ball?
一个口袋里有5个黄球，4个红球，从中任意摸一个，摸到红球的可能性是多少．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<result>4/9 = around 0.444444</result>