There are 5 red balls and 2 white balls in a bag, if one ball is randomly drawn from it, what is the probability of drawing a white ball?
袋子中有5个红球，2个白球，从中任意摸出一个球，摸到白球的可能性是多少．
<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>