The lifetimes of 80 batteries, to the nearest hour, is shown in the table opposite. a Write down the modal class for the lifetime of the batteries. b Use interpolation to find the median lifetime of the batteries. The mid-point of each class is represented by x and its corresponding frequency by

f, giving fx = 1645. c Calculate an estimate of the mean lifetime of the batteries. Another batch of 12 batteries is found to have an estimated mean lifetime of 22.3 hours. d Find the mean lifetime for all 92 batteries. Lifetime (hours) Number of batteries 6-10 2 11-15 10 16-20 18 21-25 45 26-30 5 AppendixLO1