If 9 cards of the same size and shape are marked with nine numbers from 1 to 9, what is the probability of drawing a prime number after the cards are evenly shuffled?
9张大小形状相同的纸牌，分别标有1到9九个数字，均匀洗牌后，抽到素数的可能性大小为多少．
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<result>4/9 = around 0.444444</result>