The conversation between human and AI assistant.
How many two-digit numbers can you form using the digits 1,2,3,4,5,6,7,8 and 9 without repetition?
What if we allowed repetition of digits in the two-digit numbers?
If we allowed repetition, then we would have 9 choices for each digit (since we can repeat digits). So we can form 9 x 9 = 81 two-digit numbers.