Calculate the standard deviation from the formula
The table shows the typing speed, in words per minute, of four students in a typing test, with the working for the standard deviation partly filled in
| Typing speed (wpm) | Deviation | Squared deviation |
|---|---|---|
| 45 | -2 | 4 |
| 53 | 6 | 36 |
| 45 | -2 | 4 |
| 45 | -2 | 4 |