Sumproduct To Find Average

I have 3 excel sheets (A,B and C) linked to a master sheet (X). In each sheet (A,B and C), people enter unique idetifier in first column, its type (mr, ab, J) in the second column, start date in the third column and finish date in the fourth column. At the end of every week, i subtract each start date from the finish date and get the number of days spent for each unique idetifier (column N). I preiously posted a thread (Calculate difference between dates excluding weekends) to inquire about how to calculate the difference between finish date and start date and exclude the weekends. I received some nice solutions, but none has worked as the start date cane be weekend as well.

My second and major query is once i have the difference in weekedays for each unique identifier in all the three sheets, I want to calcuate the average of each identifier type (mr, ab and J) in the master sheet. In the master sheet, i have used sumproduct to calculate the average of each idetifier type from column N for each sheet. That means i have a column for A sheet, subdivided into three types, which include the average. I am using sumproduct for this. Once this is done for each sheet type, i need a final colum in the master sheet that calculates average of all mr from A, B and C together, and similarly for ab and J. The problem here is if i combine all the sumproduct formula, i am not gettng the right answer.

My formula looks like SUMPRODUCT((SheetA!$E$5:$E$40="mr")*(SheetA!$M$5:$M$40)) for all mr in sheet A. I then divide this by SUMPRODUCT((SheetA!$E$5:$E$40="mr")*(SheetA!$M$5:$M$40<>"")) to get the average of all mrs in sheet A. I do the same for sheet B and sheet C for all three identifier types. Now i want to combine the formula for all sheets together under mr, Ab and J. I thought the following should work ((SUMPRODUCT((SheetA!$E$5:$E$40="mr")*(SheetA!$M$5:$M$40))+(SUMPRODUCT((SheetB!$E$5:$E$40="mr")*(She etB!$M$5:$M$40))+(SUMPRODUCT((SheetC!$E$5:$E$40="mr")*(SheetC!$M$5:$M$40)))/((SUMPRODUCT((SheetA!$E$5:$E$40="mr")*(SheetA!$M$5:$M$40<>""))+((SUMPRODUCT((SheetB!$E$5:$E$40="mr") *(SheetB!$M$5:$M$40<>""))+((SUMPRODUCT((SheetC!$E$5:$E$40="mr")*(SheetC!$M$5:$M$40<>""))).....
But this is giving me wrong value. It is working fine when done for individual sheets, but when combined for all three sheets together, the value is wrong.