### Instruction: How many three-digit positive integers are there?### Response: I need to count the number of ways to form a three-digit number, where the first digit cannot be zero.
The first digit can be any of the digits from 1 to 9, so there are 9 choices for it.
The second digit can be any of the digits from 0 to 9, so there are 10 choices for it.
The third digit can also be any of the digits from 0 to 9, so there are 10 choices for it.
Since the choices for each digit are independent, I can multiply the number of choices for each one to get the total number of three-digit numbers.
So the answer is 9 times 10 times 10, which is 900.