does MID() produce unsummable output?

[JackBrody]

I have digits extracted from text using MID() function. The SUM() function does not work on these digits whereas classic addition works just fine.

I enclosed the MID() function in a VALUE() fuction and it started summing up finally. But why normal addition works without this?

[mikekaganski]

MID returns a text string - read the help. There are some rules in the standard for automatic conversion, which are applicable for + and -, but not for functions. Just make sure you have numbers when you need numbers.