What are odds rolling 4 dice (common 6-sided) at same time with outcome each die is different # but cannot be "5" or "6"?

Question

The only thing I can add to question is random order.

Answer 1

Let’s call the dice A, B, C, D.

The probability of A being 1-4 is 4/6=2/3.

The probability of B being 1-4 and not being the same as A is 3/6=1/2.

The probability of C being 1-4 and being neither A or B is 2/6=1/3.

The probability of D being 1-4 and being none of A, B, C is 1/6.

The combined probability is 2/3×1/2×1/3×1/6=1/54.