There are 5 red balls and 2 yellow balls in a box, what is the probability of drawing a yellow ball?
盒子里有5个红球，2个黄球，摸出黄球的可能性是多少．
<gadget id="calculator">5 + 2</gadget>
<output>7</output>

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

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