There are 2 red balls and 5 yellow balls in a bag, what is the probability of drawing a red ball at random?
一个袋子里有红球2个、黄球5个，任意摸出一个摸到红球的可能性是多少．
<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>