It's either being used as an error checker or as a way to check for blanks.

For instance, if text appears in the P27:P117 range, it would normally cause
the whole formula to fail. The isnumber function prevents that from
happening, telling the denominator to ignore any number in N27:N117 that is
associated with a nonnumber in the P range.

Also, ISNUMBER returns a False for blank cells. So, the formula also
excludes any N27:N117 number that is associated with a blank cell in the P
range.

Looking at the whole formula, this is what appears to be happening. He wants
to divide by the sum of numbers in the N range that have a number in the P
range.

Hope that answers your question.
--
Best Regards,

Luke M
*Remember to click "yes" if this post helped you!*


"Jon" wrote:

I have opened up a worksheet that a coworker created last year and cannot
figure out the purpose of the isnumber function in this formula:
{=SUM(N27:N117*P27:P117)/SUM(N27:N117*ISNUMBER(P27:P117))}.

I have looked it up in Excel help and on Google with little insight. If
anyone can please tell me what the purpose of this function is/does, it will
be greatly appreciated. The data it is pulling from is all numbers.

Regards,

Jon