Standard +0.3 This is a straightforward chi-squared test for variance with clearly stated hypotheses and a single calculation. While it requires knowledge of the chi-squared distribution for variance testing (an S4 topic), the question is direct with no conceptual tricks—students simply need to apply the standard formula χ² = (n-1)s²/σ₀², compare to critical value, and conclude. Slightly easier than average due to its routine structure.
A mechanic is required to change car tyres. An inspector timed a random sample of 20 tyre changes and calculated the unbiased estimate of the population variance to be 6.25 minutes². Test, at the 5\% significance level, whether or not the standard deviation of the population of times taken by the mechanic is greater than 2 minutes. State your hypotheses clearly. [6]
A mechanic is required to change car tyres. An inspector timed a random sample of 20 tyre changes and calculated the unbiased estimate of the population variance to be 6.25 minutes². Test, at the 5\% significance level, whether or not the standard deviation of the population of times taken by the mechanic is greater than 2 minutes. State your hypotheses clearly. [6]
\hfill \mbox{\textit{Edexcel S4 Q2 [6]}}