hi there.

how can i add the contents of the rows given the number of rows to add?

i.e.
a1 = 1
a2 = 2
a3 = 3
a4 = 4
a5 = 5

if b1 = no of rows to add = 3
then c1 = ? formula to sum up a1:a3 = 6

if b2 = no of rows to add = 2
then c2 = ? formula to sum up a4:a5 = 9

thanks very much.