As part of a research project, the masses, \(m\) grams, of a random sample of 1000 pebbles from a certain beach were recorded. The results are summarised in the table.
| Mass (g) | \(50 \leq m < 150\) | \(150 \leq m < 200\) | \(200 \leq m < 250\) | \(250 \leq m < 350\) |
| Frequency | 162 | 318 | 355 | 165 |
- Calculate estimates of the mean and standard deviation of these masses. [2]
The masses, \(x\) grams, of a random sample of 1000 pebbles on a different beach were also found. It was proposed that the distribution of these masses should be modelled by the random variable \(X \sim N(200, 3600)\).
- Use the model to find \(P(150 < X < 210)\). [1]
- Use the model to determine \(x_1\) such that \(P(160 < X < x_1) = 0.6\), giving your answer correct to five significant figures. [3]
It was found that the smallest and largest masses of the pebbles in this second sample were 112 g and 288 g respectively.
- Use these results to show that the model may not be appropriate. [1]
- Suggest a different value of a parameter of the model in the light of these results. [2]