Problem Solving

What is the probability that one of the two integers randomly selected from range 20-29 is prime and the other is a multiple of 3?
(The numbers are selected independently of each other, i.e. they can be equal)



a) 0.06
b) 0.12
c) 0.15
d) 0.18
e) 0.20

[spoiler]
OA is b , but how?? i do not understand a part of the explanation.

Prime integers: 23 and 29. Multiples of 3: 21, 24, and 27.
The probability that the first number is prime while the second is a multiple of 3 = (2/10)*(3/10) = 0.06. [should this not be (2/10)*(3/9) ]
The probability that the first number is a multiple of 3 while the second is prime = (3/10)*(2/10) = 0.06. [should this not be (3/10)*(2/9) ]
The probability that one of the two integers is prime and the other is a multiple of 3 = 0.06 + 0.06 = 0.12 .
[and the resulting sum of probabilities= 2/15 ??][/spoiler]