



 
Hi, From your description you have a 3 digit code and a mandatory Y. The number of 3 digit codes is the number of ways of choosing 3 thing from 10 things, the ten things being 09. Mathematicians call these combinations so you want the number of combinations of 10 things taken 3 at a time, or sometimes "10 choose 3". To calculate this I suggest you look at our response to an earlier question. Penny 



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