Work with the example
Which source makes the summary show 40 minutes? The workbook opens with Summary, then Build and Input. Read the formula in Summary.B5, follow Build.B5 and finally inspect the supplied page count in Input.B5.
| Cell | Formula or source | Baseline |
|---|---|---|
| Input.B5 | 12 pages | 12 |
| Build.B5 | =Input.B5*3 | 36 minutes |
| Summary.B5 | =Build.B5+4 | 40 minutes |
Edit the working cells
Change Input.B5 to 15. Build becomes 45 and Summary becomes 49. A fresh source of zero pages gives Build 0 and Summary 4: the four-minute addition belongs to the summary formula. Inspect formulas in Calc; this exercise does not depend on Excel tracing arrows.
Check the failure case
Replacing Summary.B5 with a fixed 40 breaks the chain. It still shows 40 after the source becomes 15. Restore =Build.B5+4 to recover 49.
With Input.B5=0, why is the summary not zero?
Show the worked answer
The build is zero but the summary adds the stated four minutes.