There are 7 balls in an opaque box. There are 2 red balls, 1 yellow ball and 4 white balls. If a ball is randomly drawn from it, what is the probability that it is exactly a red ball?
在一个不透明的盒子里放有7个球，有2个红球、1个黄球、4个白球，从中任意取出一个球，正好是红球的可能性是多少
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

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