Averaging Sections of data
 

I have a daily weather data set that rannges from 1900 to 2010 with date in column A, rain (total mm for day) column B, and transpiration column c. I would like to find average transpiration for 25/11 to 5/12 (ten days), for each year and then graph accordingly.

Is this possible, its doing my head in

Cheers
ATC123

On D2, D3, D4, etc., input 10, 20, 30, so on and so forth.
On E2, the formula should have:

=AVERAGE(OFFSET(C$2,0,0,10,1))

On E3, the formula should have:

=AVERAGE(OFFSET(C$2,D2,0,10,1))