A supermarket manager wishes to make an estimate of the average time in minutes a customer spends at the checkout counter. It is known from previous studies that the variance is 9.9. How large a sample is required if she wants a 95% confidence interval for the population mean that extends no further than 1 minutes from the sample mean. Round up your answer to a whole number.
Added by Mercedes R.
Step 1
We want the confidence interval to extend no further than 1 minute from the sample mean, so we can set up the following equation: 1 = Z * (σ/√n) We know that σ (the standard deviation) is the square root of the variance, so σ = √9.9 ≈ 3.15. We also know that Show more…
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