There are 2 red balls and 5 white balls in a pocket. The balls are identical except for their color. If one ball is drawn at random, what is the probability of drawing a white ball?
口袋里有2个红球和5个白球，球除颜色外完全相同，从中任意摸出一个球，摸出白球的可能性是多少．
<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<result>5/7 = around 0.714286</result>