Rebecca recorded the time she took to travel to the gym on each of 22 days. The table gives information about these times.
| Time (x x\,x minutes) | Frequency (fff) |
|---|---|
| 0<x≤50 < x \leq 50<x≤5 | 2 |
| 5<x≤105 < x \leq 105<x≤10 | 4 |
| 10<x≤1510 < x \leq 1510<x≤15 | 3 |
| 15<x≤2015 < x \leq 2015<x≤20 | 6 |
| 20<x≤2520 < x \leq 2520<x≤25 | 5 |
| 25<x≤3025 < x \leq 3025<x≤30 | 2 |
Calculate an estimate for the standard deviation of these times. You may use ∑fx2=6587.5\sum f x^2 = 6587.5∑fx2=6587.5.
