There are 4 red balls and 5 white balls in a bag (the size and shape of the balls are the same), if you draw a ball at random, what is the probability of drawing a red ball
一个袋子里面有4个红球，5个白球(球的大小和形状一样)，任意摸出一个球，摸出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>