How to make a number out of other numbers in mathematica? I’m not entirely sure if this is possible, but I would like to make numbers composed of other numbers. For example, given $a$, $b$, and $c$, I’d like to make a number such that the digits are $a.bc$. 
So, if $a = 1$, $b = 2$, and $c = 3$, we would have the number $1.23$. Is this possible? 
Thanks!

I think what you want is:
 FromDigits[{a, b, c}] // Simplify


100 a + 10 b + c

For your example:
 FromDigits[{1, 2, 3}]/100.


1.23

