Answer to Question #293420 in Discrete Mathematics for Tege

Question

how many 2-digit or 3-digits numbers can be formed using the digits 1,2,3,4,5,6,8 and 9 if no repetition is allowed ?

Answer 1

By Combinatorial Product Rule, the number of 2-digit numbers is equal to $8\cdot 7= 56,$ the number of 3-dogit numbers is equal to $8\cdot 7\cdot 6=336.$

Then the Combinatorial Sum Rule implies that the number of 2-digit or 3-digit numbers is equal to $56+336=392.$