In the problem statement - the following sentence did not make sense to me :
“Since 27 is not divisible by 6, some permutations correspond to more ways than others, so not all permutations are equally likely”
Now since there are 27 different ways we can choose the elements - and each of these 27 are equally likely ( 1/27). Hence the probability of choosing one of the 6 valid permutations out of the 27 is also equally likely. Why why does it say not all permutations are equally likely?