how do i write a formula to do a variable sum calculation. ie i have a column
of numbers in A from A5 going down to A25. in cell F1 i have a value between
1 and 20. this example F1 = 7.
so the value in the formula would be A5+ the value in F1 (7) which would
equal A12.

so the final formual would be =sum(A5:A5+value in f1).
=sum(a5:a12)