» Summing Sales Amounts According to Product Category and Customer Name

Problem:

Columns A:C contain product categories, customer names, and prices paid for various items.
When using the following formula to sum the prices paid by Customer1 on category A products, #NUM! is returned:
=SUMPRODUCT((A:A="A")*(B:B="Customer1"),C:C)

Solution:

Use the SUMPRODUCT function as shown in the following formula:
=SUMPRODUCT((A1:A7="A")*(B1:B7="Customer1"),C1:C7)
Note:
Summing or counting according to multiple criteria cannot be performed on entire column.
Therefore, in order to use the above formula, the column ranges must be adjusted to specific ranges (i.e. A1:A10, A1:A2000, A1:A65000, etc.).