Instead of summarizing different workbooks one by one in a master worksheet, you can use consolidate workbooks feature in Excel to summarize results from different workbooks at once.
Do the following steps to easily sum, count, average, etc. to a master sheet:
1. Open all the workbooks:
Workbook 1 (Sheet 1)
Workbook (Sheet 2)
Workbook (Sheet 3)
2. Open a blank workbook, go to Data tab and click on Consolidate icon.
4. In the Reference box, select a range of cells from Sheet1 (we select D4:D7 in example) and click Add.
5. Repeat the step 4 for Sheet2 and Sheet3 workbooks.
7. Press Ok, Excel will sum up all Column D of all workbooks in master workbook.