=A1/SUM(A$1:A$100) or A1/SUM(A:A) ?
If you are getting errors, and you want the help of the group in solving
your problem, then you are more likely to get useful help if you tell the
group what errors you are getting. If you are getting error messages, tell
us what the message is. If you are getting different results what what you
expect, tell us what formula you are using, what values are in the input
cells, what value you were expecting, and what value you got. Otherwise, if
we have to guess the right question, it reduces the chances of us also
guessing the right answer.