theoretical probability algebra

Question

you spin the spinner once what is p(prime or factor of 21)

Answer 1

prime factors of 21 are 2,3,5,7,11,13,17,19,

8 of them out of 21 numbers

1, by definition, is not prime

even though it's only divisible by itself

Pr(prime)= 8/21 = about 38.1%