This document provides statistics for a sample of 50 items where xi is the value of each item and ni is the frequency of that value. It calculates the sample mean (m1) as 39 and the population mean (m2) as 1957.50. It then finds the variance (μ2) as 436.50 and the standard deviation (σ) as 20.89.

1. Exercice 18
xi ni n i xi n i xi 2
17,5 12 210 3675
30 20 600 18000
50 10 500 25000
80 8 640 51200
50 1950 97875
(a) On calcule successivement :
1950 97875
m1 = = 39 et m2 = = 1957, 50
50 50
Ainsi :
µ2 = m2 − m2 = 436, 50
1
(b) Écart type : σ = µ2 20, 89