Free practice · numeric · medium

Practice

Reconcile overlapping contact groups

Northstar's fictional contact list has 52 newsletter contacts, 31 event contacts, and 8 in both groups. How many unique contacts are in at least one group?

Category relationship map

Membership, overlap, and exclusion change the count

Membership

MemberInside

ExcludedOutside

Relationship

SubsetFully contained

OverlapShared members

Reconcile

UniqueA + B − overlap

Define each set before placing stable record identities, then reconcile overlap members exactly once in the unique total.