Question

How many 2-digit numbers can be formed using only the digits 2, 3, 5 and 6, if the numbers are not repeated within a number?

Answer 1

(1) Repetition allowed : There are 4 choices for both positions, so 4 × 4 = 16 2-digit numbers can be formed. (2) Repetition not allowed : There are 4 options for tens position, and three options for ones position. Therefore, 4 × 3 = 12 2-digit numbers can be formed.