combined mean



combined mean


nx,ny    number of people 

X mean, Y  mean     means



for example


group a

the number of people  - 35
mean  - 75


group b

the number of people  - 55
mean  - 95



combined mean = (35·75+55·95) / (35+55) = 87.22



one number was added to the data the number 60 what will be the new standard deviation

combined mean = (90·87.22+1·60) / (90+1) = 86.92










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