Formula to Average Days of Distinct Orders

OrderData.xlsx

DealerOrderMonth Order ID Days to Ship
ABC Jan 30651298 2.520138889
ABC Feb 30534745 52.49027778
ABC Feb 30534745 52.49027778
ABC Feb 30557787 39.49027778
ABC Jan 30506000 70.48958333
ABC Jan 30506000 70.48958333
ABC Jan 30503921 71.48958333
ABC Jan 30503921 71.48958333
ABC Jun 30778388 37.41527778
ABC Jun 30778388 37.41527778
ABC Jun 30778388 37.41527778
ABC May 30616742 7.490277778
ABC May 30730743 -
ABC May 30721575 53.41666667

With this info, I need to find the Monthly (Column A) average of the number of days (Column C) it took to fulfill each distinct order (Column B).

The trouble is order IDs with multiple parts are duplicated (so that there is one row per part). Because of this, I need to use the average of a distinct set of Order IDs as to not weight the averages incorrectly.

Can anyone help? Please let me know if I need to clarify anything at all.

Thanks in advance

I did the same thing Simarui suggested.

OrderData(1).xlsx

Thank you all for your input. I ended up using daffodil11's suggestion and it worked great!