Use a z-score formula:
z = (x - mean)/sd
Find the z-score that corresponds to 75% using a z-table. Remember that this value will be a positive z-score and above the mean of the distribution. Substitute z, mean, and sd given in the problem, then solve for x.
I hope this will help get you started.
An employer wants to estimate to set a time limit so that 75% of the employees will finish a job on time. Past history has shown that the time required to do the job is normally distributed and has a mean time of 26 minutes with a standard deviation of 5 minutes. How much time should the employer allow employees to finish the job? Round to the nearest minute. Show work.
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