SUMIF Mystery!

Hello,

I am using SUMIF to determine the total number of Models and Products in my spreadsheet. Column A identifies model or product with an "M" or "P". Column B contains the number of each for a particular day. I have used SUMIF to find the total of each category:

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And

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For some reason, the "M" value in A2 and the "9" value in B2 is not being included in the sum. Why is the SUMIF formula in B6 returning "5" instead of "14"?

Mystery.jpg

I can not see why this row is not being included. Download the attachment and see for yourself!

I know this may appear arbitrary - the example here is extracted from a much larger document and it took me a while to figure out why my numbers are not adding up. I have posted the question so I can figure out what is going on to prevent future errors - if I had not caught this myself by using a check column, it could have made a major problem and I am concerned with the reliability of this formula.

Thanks in advance for your help folks.
- N2SO

Or if they should only be M or P, you could use a wildcard:

=SUMIF(A1:A5,"M*", B1:B5)