skipping sums across worksheets

I have been combing the forums for an answer but feel there may be an easier way to solve my problem without learning arrays, etc. (hopefully!). I have some data on one sheet and I am trying to represent the sum of data on another sheet. I realize for one instance of summing I could complete by writing "=SUM(data!B3:B4)." However, if I want the cell below the previous one to indicate "=SUM(data!B5:B6)." Here is where I run into my dilemma. When I drag for formula down to populate the column it doesn't skip what has been summed already and would provide =SUM(data!B4:B5), then =SUM(data!B5:B6), etc. How does the logic change for including the sum of three or four at a time without the same overlapping problem when the formula is dragged down? Any help would be appreciated; many thanks.

Try this in B3 and filled down

=SUM(OFFSET(data!$B$3:$B$4,(ROWS(A$1:A1)-1)*2,0))

Don't change the A$1:A1 reference, it is not related to your data.
The *2 represents the interval.

So if you wanted to do every 3 rows, adjust the initial range to B3:B5 and change the *2 to *3

Thank you Jonmo1 and JieJenn! You have just saved me hours of manual input!

Great, glad to help out.