Answer:
a. 99
b. 12.31
Step-by-step explanation:
a. Estimate of the population mean number of units sold per month
n = Number of Data Values = 5
Sum of Data Values = Σxi =97 + 120 + 88 + 97 + 93 =  495
Sample Mean = X = Σxi/n = 495 / 5 = 99
The population mean number of units sold per month is 99
b. Estimate of the population standard deviation
Month   Data (x)   X   x - X   (x - X)^2
  1       97      99   -2     4
  2       120     99    21    441
  3       88     99    -11    121
  4       97     99    -2     4
  5       93     99    6     36
Sum of deviation squared      606
s^2 = Sample Variance = Σ(xi - X)2/(n - 1)
Sample Variance = 606/4 = 151.5
Sample Standard Deviation = √Sample Variance
Sample Standard Deviation = √151.5
Sample Standard Deviation = 12.30853362509117
Sample Standard Deviation = 12.31
The point estimate of the population standard deviation is 12.31
