How many even numbers less than 500 can be formed using the digits 1, 2, 3, 4 and 5? Each digit may beused only once in any number.

To solve this problem, we need to consider the different cases for the number of digits in the number.

1. One-digit numbers: The only even one-digit number is 2. So, there is 1 such number.

2. Two-digit numbers: The units place must be an even number. So, there are 2 choices (2 and 4) for the units place. The tens place can be any of the remaining 4 digits. So, there are 4 choices for the tens place. Therefore, there are 2*4 = 8 such numbers.

3. Three-digit numbers: Again, the units place must be an even number. So, there are 2 choices for the units place. The hundreds place can be any of the remaining 4 digits, so there are 4 choices for the hundreds place. The tens place can be any of the remaining 3 digits, so there are 3 choices for the tens place. Therefore, there are 243 = 24 such numbers.

4. Four-digit numbers: The units place must be an even number. So, there are 2 choices for the units place. The thousands place can be any of the remaining 4 digits, so there are 4 choices for the thousands place. The hundreds place can be any of the remaining 3 digits, so there are 3 choices for the hundreds place. The tens place can be any of the remaining 2 digits, so there are 2 choices for the tens place. Therefore, there are 243*2 = 48 such numbers.

5. Five-digit numbers: The units place must be an even number. So, there are 2 choices for the units place. The ten thousands place can be any of the remaining 4 digits, so there are 4 choices for the ten thousands place. The thousands place can be any of the remaining 3 digits, so there are 3 choices for the thousands place. The hundreds place can be any of the remaining 2 digits, so there are 2 choices for the hundreds place. The tens place can be the remaining 1 digit, so there is 1 choice for the tens place. Therefore, there are 24321 = 48 such numbers.

Adding up all these cases, there are 1 + 8 + 24 + 48 + 48 = 129 even numbers less than 500 that can be formed using the digits 1, 2, 3, 4, and 5 each only once.