Hi Mr F

1. Yes you're right - it's 3 of each colour - sorry.
2. I had assumed that the answer would be more than 20 factorial, because it would be 20 factorial if they ordered 20, and thay can order 60 (although the number of colours remain cosntant at 20). I'm afraid I'm a beta-brain!
3. Thank you for your answer - which is clearly billions, even in the old-fashioned UK definition of 10 to the 12th.

James