Average of the sum of two columns

[firen66]

Hi there!
Probably there is a very simple formula for this, but I'm quite new to spreadsheets :/

Given the example in the picture, where C is the sum of A and B, is there a way I can get D1 without actually creating the column C?

Thanks in advance!

Screen Shot 2018-08-29 at 17.59.40.png

[modytrane]

How about:

=Average(A1:B13)*2

[firen66]

Seems to do it!

[modytrane]

You wanted average of all the sums, which is same as adding all the numbers in columns A and B; then calculate average.
Now you want to divide by half as many data points, which is same as dividing by total numbers of data points and multiplying by 2.