Exercise In a research, the lifetime of 60 generators ( in hours) were recorded and the results are shown in the first two columns of the following table. Classes Frequency Mid-points (x;) 10-20) 5 20-30 8 30-40) 12 (40-50) 18 50-60) 11 60-70 6 Total 60 Table: Calculation of the mean lifetime of generators 1. Fill out the table and calculate the mean lifetime of a generator. 2. Calculate the variance and the standard deviation of the data. 3. Construct the histogram of the data and comment on its shape