There are several balls of red, yellow, and blue in a box. The ratio of the number of red balls, yellow balls, and blue balls is 3:4:5. Randomly draw a ball from this box, and draw a red ball. What is the probability of the ball.
在一个盒子里有红、黄、蓝三种颜色的球若干个，红球、黄球和蓝球的个数比是3：4：5，从这个盒子里任意摸出一个球，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>