Write all 4-digit numbers that can be formed with the digits 2 and 5, using both digits equal number of time. Also find their sum.

We are required to write 4-digit numbers using only the digits 2 and 5, with each digit used the same number of times. So each digit is used twice.

The digits to be arranged are 2, 2, 5 and 5.

The possible 4-digit numbers are:

2255, 2525, 2552, 5225, 5252, 5522.

Sum = 2255 + 2525 + 2552 + 5225 + 5252 + 5522

= 23,331

Hence, the required 4-digit numbers are 2255, 2525, 2552, 5225, 5252 and 5522, and their sum is 23,331.