1. Lena is analyzing how long it takes to make cheesecakes at her restaurant. The preparation consisted in four elements and the study included 20 job cycles. The cumulative times and performance rating factors for each element are as follows:

Assuming an allowance factor of 20%, calculate:

1. The normal time for the job.

2. The standard time for the job.

3. How many observations does Lena need to take if she wants to be 95% confident she is within 4% of the actual preparation time? Assume that the average job cycle time is 2.67 min, and the standard deviation of the sample is 0.72 min.