| Exam Board | Edexcel |
|---|---|
| Module | S3 (Statistics 3) |
| Year | 2007 |
| Session | June |
| Marks | 6 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Confidence intervals |
| Type | CI with two different confidence levels same sample |
| Difficulty | Standard +0.3 This question requires understanding the relationship between confidence intervals and critical values, then working backwards from a 99% CI to find the standard error, and forwards to construct a 95% CI. It's a standard S3 confidence interval manipulation requiring knowledge that CI width is proportional to z-values, but the multi-step calculation and conceptual understanding needed makes it slightly easier than average for A-level. |
| Spec | 5.05d Confidence intervals: using normal distribution |
\begin{enumerate}
\item A random sample of the daily sales (in £s) of a small company is taken and, using tables of the normal distribution, a 99\% confidence interval for the mean daily sales is found to be\\
(123.5, 154.7)
\end{enumerate}
Find a $95 \%$ confidence interval for the mean daily sales of the company.\\
(6)\\
\hfill \mbox{\textit{Edexcel S3 2007 Q6 [6]}}