Applying the sum function to non-consecutive blocks of cells

Hi all,

I'm trying to use the sum formula to add up blocks of 15 cells at a time. For example, I want to add E1:E15; then E16:E30; then E31:E45. If I type in =sum(E1:E14), and then copy the formula and apply it to the next cell, it returns the sum of E2:15. In other words, Excel will add up 15 cells, but not the 15 cells I want it to add up. What kind of command can I use to tell Excel to sum up certain blocks of cells?

Thanks!

-Rose

ie range data at E1:E45

first formula

=SUM(OFFSET($E$1,(ROW(1:1)-1)*15,,15))

copy down

Thanks so much! This works perfectly.

Now I'd like to do the same thing, except with 8 cells at a time and calculating the 95% confidence interval instead of just the sum. The formula I am using is: confidence(0.05,A1,8) where A1 would be the cell that contains standard deviation, and 8 is the sample size. How can I apply this to a 8 cells, then the next 8 cells, then so on?

Try this
=confidence(0.05,Offset(A1,(Row(A1)-1)*8),8)
drag down.

Actually I realized that I need to do that for the standard deviation, not the confidence interval, so I went back and modified the sum offset function the previous user posted. Then I made another column for confidence interval and simply referred to the standard deviation cell, and copied that down. Thanks so much for your help.