Question

A researcher wants to estimate the mean age of all Business Week readers at a 99% confidence level. The standard deviation of ages of all Business Week readors is nine years. The sample size that will yield a maximum error of estimate within three years of the population mean is at least:
A. 60
B. 97
C. 185
D. 8

Answer 1

Answer:

A. 60

Step-by-step explanation:

We have that to find our $\alpha$ level, that is the subtraction of 1 by the confidence interval divided by 2. So:

$\alpha = \frac{1-0.99}{2} = 0.005$

Now, we have to find z in the Ztable as such z has a pvalue of $1-\alpha$.

So it is z with a pvalue of $1-0.005 = 0.995$, so $z = 2.575$

Now, find the margin of error M as such

$M = z*\frac{\sigma}{\sqrt{n}}$

In which $\sigma$ is the standard deviation of the population and n is the size of the sample.

We have to find:

n when $M = 3, \sigma = 9$. So

$M = z*\frac{\sigma}{\sqrt{n}}$

$3 = 2.575*\frac{9}{\sqrt{n}}$

$3\sqrt{n} = 9*2.575$

Dividing both sides by 3

$\sqrt{n} = 3*2.575$

$(\sqrt{n})^{2} = (3*2.575)^{2}$

$n = 59.68$

We round up, so the correct answer is:

A. 60