There are 7 yellow balls, 2 green balls, and 1 red ball in a box. If you touch the green ball and win the prize, what is the probability of winning?
一个盒子里有7个黄球、2个绿球、1个红球，摸到绿球中奖，中奖的可能性是多少
<gadget id="calculator">7 + 2 + 1</gadget>
<output>10</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>