I've 2 columns A and B of which Column A contains letters and Column B
contains Numbers. I would like to know a formula which would find the
average of column B but exclude the row if Column A contains "aaa"

Example:
aaa 10
aab 12
aac 10
aad 12
aae 10
aaf 1
aag 0
aah 11
I would want the formula to skip the 1st row which has 'aaa' in column A.

Thanks in advance.
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Karthi