An opaque pocket contains 3 red balls and 1 yellow ball. Xiao Ming puts a ball back into the bag after he has touched it 3 times in a row, and all he has touched are red balls. Now he is going to touch the 4th time. What is the probability that he will touch a yellow ball this time?
一个不透明的口袋中装有3个红球.1个黄球．小明每次摸出一个球后又放回袋中，他连续摸了3次，摸到的都是红球，现在他准备摸第4次，他这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>