There are 8 red balls and 5 white balls in a box. If a ball is randomly drawn from it, what is the probability of drawing a red ball?
盒子里有8个红球、5个白球，从中任意摸出一个球，摸到红球的可能性是多少．
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">8 / 13</gadget>
<output>8/13 = around 0.615385</output>

<result>8/13 = around 0.615385</result>