There are 3 red balls and 1 yellow ball in a pocket. (Each time he touches a ball and puts it back in the pocket) Xiao Ming touches a red ball three times, so what is the probability of the fourth touch of a yellow ball?
一个口袋中装有红球3个、黄球1个，(每次摸一个球再放回口袋中)小明摸了三次都是红球，那么第四次摸到黄球的可能性是多少
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

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

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