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Set by the statistical distribution of the sample.
x_i 11 12 13 14 15 16 17 18 19
n_i 3 8 10 55 12 5 3 2 2
n_i x_i 33 96 130 770 180 80 51 36 38
x_i ^ 2 121 144 169 196 225 256 289 324 361
n_i 〖〗 x_i ^ 2 363 1152 1690 10780 2700 1280 867 648 722

Define:
a) the sample mean,
b) the sample variance,
c) sample standard deviation.

Ready, solving problems in mathematical statistics