Smalawi,

That is not how Fill works.

I think you should look into using a pivot table for this. It will to all
of the calculations you need with out much work from you,

Look up pivot tables in XL's help and learn as much about using them as you
can.
-select all of your data (or just one cell in your data)
-(in XL 2002/2003) Click Data menu PivotTable and PivotChart Report...
(don't know XL 2007)
-You'll probably be save selecting all of the defaults and clicking finish
right from the get-go.
-Add your "Year" column to the "Row" section of the pivot table
-Add the "Temp" column to the "Data" section of the pivot table
-Change the Temp column properties to average instead of sum.

HTH,

Conan




"Smalawi" wrote in message
...
Hi, ive been asked to work out the average temperature for every year from
1880-2007. The problem i have is when i put in the normal =sum(a1:a12)/12
i
need it to fill the formula so the next one is =sum(a13:a25)/12 and then
the
next one is =sum(a26:38)/12 etc etc ,when i try it excel doesnt remember
the
adding together the next set of 12 bit. If anyone could help it would save
me
loads of time
Cheers!


Year Month Temp Precipitation
1880 1 -5.2 17.7
1880 2 1.7 31.1
1880 3 7.6 14.5
1880 4 10.1 32.8
1880 5 13.2 11.5
1880 6 15.2 53.1
1880 7 19.1 42.1
1880 8 17.2 65.9
1880 9 14.6 56.8
1880 10 9.2 38.7
1880 11 2.9 64.5
1880 12 1.1 63.9
1881 1 -3.7 79.7
1881 2 1.6 33.8
1881 3 6 55.3
1881 4 9.8 16.7
1881 5 13.4 20.1
1881 6 16.8 16.1
1881 7 21 43.3
1881 8 17.9 129.8
1881 9 12.4 34.5
1881 10 5.7 34.4
1881 11 4.2 13.1
1881 12 -1.5 13.5
1882 1 -1.9 2.8
1882 2 0.9 6.4
1882 3 6.8 7.2
1882 4 9.4 18.1
1882 5 13.9 16.1
1882 6 15.8 33.7
1882 7 16.6 55.3
1882 8 16 91.4
1882 9 11.7 147.3
1882 10 8.9 77
1882 11 2.4 136.7
1882 12 0.1 103.1