Question

The operations manager at a compact fluorescent light bulb (CFL) factory needs to estimate the mean life of a large shipment of CFLs. The manufacturer’s specifications are that the population standard deviation is 1,000 hours. A random sample of 64 CFLs indicated a sample mean life of 7,500 hours.
Construct a 95% confidence interval estimate for the popu- lation mean life of compact fluorescent light bulbs in this shipment.

Answer 1

Answer:

The 95% confidence interval estimate for the population mean life of compact fluorescent light bulbs in this shipment is between 7,255 hours and 7,745 hours.

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:

$\alpha = \frac{1-0.95}{2} = 0.025$

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 $1-0.025 = 0.975$, so $z = 1.95$

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.

$M = 1.96*\frac{1000}{\sqrt{64}} = 245$

The lower end of the interval is the sample mean subtracted by M. So it is 7500 - 245 = 7255 hours.

The upper end of the interval is the sample mean added to M. So it is 7500 + 245 = 7745 hours.

The 95% confidence interval estimate for the population mean life of compact fluorescent light bulbs in this shipment is between 7,255 hours and 7,745 hours.