There are 7 red balls and 6 white balls in a box, if you touch any ball, what is the probability of getting a red ball?
盒子里有7个红球，6个白球，任意摸一个球，摸到红球的可能性是多少．
<gadget id="calculator">7 + 6</gadget>
<output>13</output>

<gadget id="calculator">7 / 13</gadget>
<output>7/13 = around 0.538462</output>

<result>7/13 = around 0.538462</result>