To find the number of different four-digit numbers that can be formed using the digits 2, 3, 4, 7, and each digit used only once, you can use the counting principle.
There are four positions in a four-digit number, and for each position, you have a choice of four different digits (2, 3, 4, and 7) since each digit can only be used once.
So, for the first position, you have 4 choices, for the second position, you have 3 choices (since one digit has already been used), for the third position, you have 2 choices, and for the fourth position, you have 1 choice.
Now, multiply the choices together to find the total number of different four-digit numbers:
Total = 4 (choices for the first position) × 3 (choices for the second position) × 2 (choices for the third position) × 1 (choice for the fourth position)
Total = 4 × 3 × 2 × 1 = 24
So, there are 24 different four-digit numbers that can be formed using the digits 2, 3, 4, and 7, with each digit used only once.