9231 P41 - Nov 2024 - Q1 - 6 marks
6839
Ellie is investigating the heights of two types of beech tree, \(A\) and \(B\), in a certain region. She has chosen a random sample of 60 beech trees of type \(A\) in the region, recorded their heights, \(x \mathrm{~m}\), and calculated unbiased estimates for the population mean and population variance as 35.6 m and \(4.95 \mathrm{~m}^{2}\) respectively.
Ellie also chooses a random sample of 50 beech trees of type \(B\) in the region and records their heights, \(y \mathrm{~m}\). Her results are summarised as follows.
\(\sum y=1654 \quad \sum y^{2}=54850\)
Find a \(95 \%\) confidence interval for the difference between the population mean heights of type \(A\) and type \(B\) beech trees in the region.
Solutions and mark schemes for 9231 are temporarily available to admins only.