5 The table shows the mean and standard deviation of the weights of some turkeys and geese.
| Number of birds | Mean (kg) | Standard deviation (kg) |
| Turkeys | 9 | 7.1 | 1.45 |
| Geese | 18 | 5.2 | 0.96 |
- Find the mean weight of the 27 birds.
- The weights of individual turkeys are denoted by \(x _ { t } \mathrm {~kg}\) and the weights of individual geese by \(x _ { g } \mathrm {~kg}\). By first finding \(\Sigma x _ { t } ^ { 2 }\) and \(\Sigma x _ { g } ^ { 2 }\), find the standard deviation of the weights of all 27 birds.