A major electronics store chain is interested in estimating the average amount its credit card customers spent on their first visit to the chain's new store in the mall. Fifteen credit card accounts were randomly sampled and analyzed with the following results: $\bar { x }$ = $50.50 and s² = 400. A 95% confidence interval for the average amount the credit card customers spent on their first visit to the chain's new store in the mall is: A)$50.50 $\pm$ $9.09. B)$50.50 $\pm$ $10.12. C)$50.50 $\pm$ $11.08. D)None of these choices.

Question

Quizplus · Accepted Answer

The confidence interval is calculated using the formula $\bar{x} \pm t \times \frac{s}{\sqrt{n}}$. With $\bar{x} = 50.50$, $s^2 = 400$ (so $s = 20$), $n = 15$, and using a t-value for 14 degrees of freedom at 95% confidence, the interval is $50.50 \pm 11.08$.

A Major Electronics Store Chain Is Interested in Estimating the Average