There are 7 white balls, 5 red balls and 3 yellow balls in a pocket. They are identical except for their color. If you draw a ball randomly, what is the probability of getting a red ball?
口袋里有7个白球，5个红球和3个黄球，它们除颜色外完全相同，从中任意摸出一个球，摸到红球的可能性是多少．
<gadget id="calculator">7 + 5 + 3</gadget>
<output>15</output>

<gadget id="calculator">5 / 15</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>