13 A seed company investigated how well African Marigold seeds germinated when the seeds were past their sell-by date. The table shows the average number of seeds which germinated per packet, \(y\), and the number of months past their sell-by date, \(t\).
| \(t\) | 10 | 20 | 30 | 40 | 50 |
| \(y\) | 24.5 | 24.0 | 21.7 | 18.6 | 12.4 |
The summary data for the investigation were as follows.
$$\Sigma t = 150 \quad \Sigma t ^ { 2 } = 5500 \quad \Sigma y = 101.2 \quad \Sigma y ^ { 2 } = 2146.86 \quad \Sigma t y = 2740$$
- Calculate the equation of the regression line of \(y\) on \(t\).
- Use your regression line to calculate \(y\) when \(t = 10\). Compare your answer with the value of \(y\) when \(t = 10\) in the table and comment on the result.
- Use your regression line to calculate \(y\) when \(t = 100\). Comment on the validity of this result.
- Suggest with reasons whether the regression line provides a good model for predicting the germination of seeds past their sell-by date.