Distinct Customers per Region (No Helper Column)

You're a marketing analyst pulling tomorrow's territory readout. The order log at A2:B25 records (Region, Customer) for every order — and customers typically order multiple times per region across the quarter, so the table has heavy duplication. You need the count of distinct customers for each of the three regions in D2:D4.

Two acceptable approaches — pick whichever you're more comfortable with under the timer:

• Modern (Excel 365 / 2021+): =COUNTA(UNIQUE(FILTER($B$2:$B$25, $A$2:$A$25=D2))) — three function calls.
• Classic array trick: =SUMPRODUCT(IFERROR(($A$2:$A$25=D2) / COUNTIFS($A$2:$A$25, D2, $B$2:$B$25, $B$2:$B$25), 0)) — for each row in the target region, contribute one over the count of (target region, that customer) combos. Each unique customer sums to exactly 1.

The IFERROR is necessary in the legacy version because COUNTIFS returns 0 for rows whose customer doesn't appear in the target region — division by zero would otherwise produce #DIV/0! and corrupt SUMPRODUCT.

Your task:

1. In column E (Distinct Count), write a formula that returns the integer distinct-customer count for each region in column D.

Graded cells: E2, E3, E4.