The ratio of red, yellow and blue balls in a box is 3:4:5. Randomly draw a ball from the box, what is the probability of drawing a red ball?
在一个盒子里红、黄、蓝球的个数比为3：4：5．从盒子里任意摸出一个，摸出红球的可能性是多少．
<gadget id="calculator">3 + 4 + 5</gadget>
<output>12</output>

<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>