» Avoiding Errors When Counting Date Values That Meet Specified Criteria

Problem:

The range A2:B9 contains a series of dates and the corresponding number of hours worked on each of them.
An empty cell in column B that matches a date in column A indicates that 0 hours were worked on that day.
The range may also include blank rows.
The following formula was created to count the number of days in January for which 0 hours were worked:
=SUMPRODUCT((MONTH(A2:A9)=1)*(ISBLANK(B2:B9)))
However, an incorrect result of 3 was returned.

Solution:

Use the SUMPRODUCT, MONTH, ISBLANK, and ISNUMBER functions as shown in the following formula:
=SUMPRODUCT((MONTH(A2:A9)=1)*(ISBLANK(B2:B9))*(ISNUMBER(A2:A9)))


Date_____Hours Worked
1 Jan____8

4 Apr____5
3 Mar____4

5 Jan
8 Feb
10 Jan___2
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