Six 6-sided dice are rolled. What is the probability that three of the dice show prime numbers and the rest show non-prime numbers?

Im not too good at probability, but there is a 3/6 chance of it being a prime number (2,3,5) so that would be (3/6)^3 chance of the first 3 being prime, and then a (3/6)^3 for it not to be a prime number. so that would be (3/6)^6

Primes are 2,3 and 5 = 1/2 chance of showing a prime

Nonprimes are 1, 4, 6 = 1/2 chance of showing a non-prime

P (that three show primes ) = C(6,3) ( 1/2)^3 ( 1/2)^3 = 20 * (1/8)^2 = 20/64 = 5/16