Dear Excel maniacs,

I need to do the sumif of certains cells combined with some kind of Vlookup in separate sheets, with duplicate values included.
I have three lists for that. The objective is to add all values per customers according to its group.

I have attached a file that describe exactly the problem (the only difference is that the lists are on the same sheet) I face to help you understanding my task.
I need to fill I4 and I5.

Sum help.xlsx

Basically :
- List 1 is where all customers are listed with their value. It is an automatic list and I can not edit it.
- List 2 is a corresponding table customer/group which is supposed to help finding the customer reference. It cannot be edited. Please note that the same customer can appear several times.
- List 3 is a consolidated view of the groups, where I have to do the sum of the customers value.

I cannot use a pivot table or VBA for doing the job. I need a formula... I have tried to look for a SUMIFS or some weird array formula, but my knowledge of Excel is way too limited to do that. Thanks a lot in advance for your kind help !