The number of four digit numbers can be formed by using the digits 2, 3, 5, 6, 8 if at least one digit is repeated.

Given digits are $2,4,5,6,8$

If all repeated :-

We can fill each bon in 5 ways

Total number of ways $=5^4$

No one repeated:

We can fill the box $5\times 4\times 3\times 2=5!$ways

At least one letter is repeated, we can arrange $5^4-5!$ ways