How spread out the numbers are, in squared units.
Two suppliers can average the same lead time and behave completely differently. Put the variance of these five lead times in B7.
Solve it on your own to keep the bonus. Each hint gets one step closer to the formula.
The same formula in the other shapes it takes at work.
This is the grid you start with. Cell references in the task — B6, C2 — point at the row numbers and column letters below.
| A | B | |
|---|---|---|
| 1 | Month | Lead time (days) |
| 2 | January | 9 |
| 3 | February | 14 |
| 4 | March | 7 |
| 5 | April | 16 |
| 6 | May | 4 |
| 7 | Variance |
These lead times average exactly 10 days, but they run from 4 to 16 — this supplier is not reliable, and the mean alone would never have said so. Variance puts a number on that spread. Its one awkwardness is the units: squaring the distances leaves the answer, 24.5, in days-squared, which nobody can picture. STDEV, next, exists to fix precisely that.