Write the six numbers 21, 23, 27, 39, 47, and 49 on the six faces of a cube, throw the cube upwards arbitrarily, what is the probability that the number facing up after falling is a prime number
在一个正方体的六个面上分别写上21、23、27、39、47、49这六个数，把这个正方体任意上抛，落下后朝上的数是素数的可能性是多少
<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

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