Marking duplicates if condition

Hello Guys!

I just found this great place
I look for some answer but I can not do it.

I need to mark duplicates using some if condition.
The formula I looking for is showed in the picture below.

Excel.PNG

One user can have the same number, but different users cannot have it.
How to solve it using simple formulas in excel?

A picture gives us nothing to work with because we can't see where your data is located.

Assuming that your sample table is in B2:C8, applying conditional formatting using the following formula as a rule will highlight the same as your sample.

=COUNTIFS($B$1:$B$8,"<>"&$B2,$C$1:$C$8,$C2)

For more on conditional formatting and how to apply it, have a look at https://support.office.com/en-us/art...b-f1951ff89d7f