dividing whit number from second table

I have:

1 table with a lot of records containing at least the name of a person and a field containing a number (this person can appear in this table many times). 

Second table with one record for each person containing name and a value. 

I want to make a calculation where the sum of the number for one person is divided bij number in the second table on the record for the specific person.

There is a many to 1 relation on the name field

There has to be an aggretation (Max, min or sum) to make the formula.  How can I use only the number from this column and not a sum  or max?