There are 4 red balls, 2 white balls and 1 yellow ball in a bag. If you touch any one of them, what is the probability of getting a white ball?
一个袋子里有4个红球，2个白球，1个黄球．从中任意摸1个，摸到白球的可能性是多少
<gadget id="calculator">4 + 2 + 1</gadget>
<output>7</output>

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

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