There are 5 black balls and 4 white balls of the same shape in a box, what is the probability of drawing a black ball?
一个盒子里有形状完全相同的5个黑球与4个白球，摸到黑球的可能性是多少．
<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>