Duplicates within a calendar week

[IRJULIE]

Hi everyone!

First time posting here so please excuse my ignorance...

I am trying to find a formula or conditional formatting option to highlight rows of duplicate data that occur within a calendar week (Monday-Sunday). I have only 2 columns of data; column A is a serial number and column B is a date. All dates fall within the same month and each serial number should occur once in each calendar week for the month (though occasionally not for every week).

Serial A	3/11/2020​
Serial A	10/11/2020​
Serial A	17/11/2020​
Serial A	24/11/2020​
Serial A	25/11/2020​
Serial B	4/11/2020​
Serial B	11/11/2020​
Serial B	18/11/2020​
Serial B	20/11/2020​
Serial B	25/11/2020​

In this example, both Serial A and Serial B have 2 dates occurring in the same calendar week (Serial A 24/11/20 & 25/11/20; Serial B 18/11/20 & 20/11/20). I need a way to highlight one or both rows with dates occurring in the same week for each serial number.

Any help would be greatly appreciated!!

 

[arthurbr]

Perhaps create a helper column in col C ( can be hidden) with the formula =WEEKNUM($B1;2) and pull down
Then use =SUMPRODUCT(--($A$1:$A$10=$A1),--($C$1:$C$10=$C1))>=2 as formula for your CF