in column a1:a25 i have the following values

a1 r
a2 1
a3 2
a4 3
a5 4
a6 r
a7 1
a8 2
a9 3
a10 4
a11 x
a12 1
a13 2
a14 3
a15 4
a16 r
a17 1
a18 2
a19 3
a20 4
a21 x
a22 1
a23 2
a24 3
a25 4

what i want to do is caluclate the total sum if the criteria meets say x or
r.

a1, a6, a11, a16, a21

so a1, a6, a16 all = r then i want the total of a2:a5 + a7:a10 + a17:a20

and the same in another formula looking for the x criteria which would be
a11 and a21, total a12:a15 + a22:a25

this is an example, the data continues almost to the limit of rows in
excel. And some the crteria is not just x or r there are others.

any ideas?