You know how you can set an entire column with the same formula by dragging at the bottom right hand corner of a formulized block... well I need help with a formula. Its a bit complicated to explain, but I'll try my best.

I want a formula that will keep the running averages.

100 ave: 100.0
105 ave: 102.5
180 ave: 128.3
100 ave: 121.3

When I type in =AVERAGE(A1:A2)

then I drag down the formula to affect the other lines...

I want them to show

=AVERAGE(A1:A3)
=AVERAGE(A1:A4), etc...

but it ends up showing

=AVERAGE(A2:A3)
=AVERAGE(A3:A4)

Please help.