In base b, there are exactly one hundred three-digit numbers whose digits are all distinct. (That's "one hundred" in the ordinary sense, 100 base 10.) What is b?
In base 10 there are 10 distinct digits 0,1,2,3,4,5,6,7,8,9
In base 3 there are 3 distinct digits 0,1,2
In base 27 there are 27 distinct digits
Now you can answer yourself
+47 
