## The concentration of carbon monoxide (CO) in a gas sample is measured by a spectrophotometer and found to be 85 ppm. Through long experience

The concentration of carbon monoxide (CO) in a gas sample is measured by a spectrophotometer and found to be 85 ppm. Through long experience with this instrument, it is believed that its measurements are unbiased and normally distributed, with an uncertainty (standard deviation) of 9 ppm. Find a 95% confidence interval for the concentration of CO in this sample. Round the answers to two decimal places. The 95% confidence interval is

## Answers ( )

Answer:The confidence interval is , in which n is the size of the sample.

Step-by-step explanation:We have that to

findour level, that is the subtraction of 1 by the confidence interval divided by 2. So:Now, we have to find z in the Z-table as such z has a p-value of .That is z with a pvalue of , so Z = 1.96.

Now, find the margin of error M as suchIn which is the standard deviation of the population and n is the size of the sample.

The

lower endof the interval is the sample mean subtracted by M. So it isThe

upper endof the interval is the sample mean added to M. So it isThe confidence interval is , in which n is the size of the sample.