3 The times, \(t\) minutes, taken to complete a walking challenge by 250 members of a club are summarised in the table.
| Time taken \(( t\) minutes \()\) | \(t \leqslant 20\) | \(t \leqslant 30\) | \(t \leqslant 35\) | \(t \leqslant 40\) | \(t \leqslant 50\) | \(t \leqslant 60\) |
| Cumulative frequency | 32 | 66 | 112 | 178 | 228 | 250 |
- Draw a cumulative frequency graph to illustrate the data.
\includegraphics[max width=\textwidth, alt={}, center]{1eb957f4-5088-4991-aa8a-f895d55d2bcf-04_1395_1298_705_466} - Use your graph to estimate the 60th percentile of the data.
It is given that an estimate for the mean time taken to complete the challenge by these 250 members is 34.4 minutes. - Calculate an estimate for the standard deviation of the times taken to complete the challenge by these 250 members.