Suppose the investigator believes that virtually all values of breakdown voltage are between 40 and 70. What sample size would be appropriate for the 95% CI to have a width of 2 kV? (so that m is estimated to within 1 kV with 95% confidence)

The sample size required is 865.

Step-by-step explanation:

The (1 - α)% confidence interval for population mean is:

The margin of error of this interval is:

It is provided that all values of breakdown voltage are between 40 and 70.

So, the minimum value of breakdown voltage is, Min. = 40 and the maximum value of breakdown voltage is, Max. = 70.

Assume that the population standard of the distribution of breakdown voltage is known.

The standard deviation is:

The margin of error is, MOE = 1 kV.

The critical value of z for 95% confidence level is:

Compute the sample size as follows:

Thus, the sample size required is 865.