4 The times taken, in minutes, to complete a word processing task by 250 employees at a particular company are summarised in the table.
| Time taken \(( t\) minutes \()\) | \(0 \leqslant t < 20\) | \(20 \leqslant t < 40\) | \(40 \leqslant t < 50\) | \(50 \leqslant t < 60\) | \(60 \leqslant t < 100\) |
| Frequency | 32 | 46 | 96 | 52 | 24 |
- Draw a histogram to represent this information.
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From the data, the estimate of the mean time taken by these 250 employees is 43.2 minutes. - Calculate an estimate for the standard deviation of these times.