This is a recent thread doing a similar thing.
To randomly select 5 or 15 rows from three sets of 20 in a single loop will definitely need a code component, but you should start with Builder and then customise it.
This is a recent thread doing a similar thing.
To randomly select 5 or 15 rows from three sets of 20 in a single loop will definitely need a code component, but you should start with Builder and then customise it.