How many four-digit odd numbers can be formed with the digits 0-9 if each digit is used only once in each number?

Sure, here is the step by step solution:

Step 1: Since the number is odd, the unit place can be filled by any one of the 5 odd numbers (1, 3, 5, 7, 9). So, there are 5 ways to fill the unit place.

Step 2: The thousands place (the first digit) can't be 0 (since it's a four-digit number) and it can't be the same as the unit place digit. So, there are 8 ways to fill the thousands place.

Step 3: For the hundreds place (the second digit), we can't use the digit we used for the thousands place or the unit place, and it can be 0. So, there are 8 ways to fill the hundreds place.

Step 4: For the tens place (the third digit), we can't use the digits we used for the thousands place, the hundreds place, or the unit place. So, there are 7 ways to fill the tens place.

Step 5: Multiply the number of ways to fill each place together to get the total number of four-digit odd numbers. So, the total number of four-digit odd numbers is 5 * 8 * 8 * 7 = 2240.