Hi ,
The formulas in the range C4:C38 are not all identical ; the range used in the first 33 formulas is $B$4:$B$37 , while that in the last 2 formulas is $B$4:$B$38.
If you correct the first 33 formulas so that they also refer to the range $B$4:$B$38 , then the two averages will be identical.
Narayan