» Retrieving the Column Header that Corresponds with a Matched Value

Problem:

Looking up the range A2:C5 for each of the values listed in column E, and retrieving the corresponding column header for each match.

Solution:

Use the INDEX, SUMPRODUCT, MAX, and COLUMN functions as shown in the following formula:
=INDEX($A$1:$C$1, SUMPRODUCT(MAX(($A$2:$C$5=E2)*(COLUMN($A$2:$C$5))))-COLUMN($A$1)+1)