How to condense several rows into fewer rows?

[Admin]

Hi gavin_machine,

Welcome to ExcelFox !!!

I assume your data in A2:A11,

In B2 and copied down,

=AVERAGE(INDEX($A$2:$A$11,ROWS($B$2:B2)*$C$1-1):INDEX($A$2:$A$11,ROWS($B$2:B2)*$C$1))

where C1 holds the interval

HTH