Question

the mean score of 25 observations is 80. the mean score of another 55 is 65. determine the mean score of the whole set of observations

Answer 1

Given mean of 25 observations = 80
Mean = (sum of observations)/(number of observations)
80 = (sum of observations)/25
Hence sum of observations = 80 x 25 = 2000
Similarly sum of observations of other data = 55 x 65 = 3575
Sum of observations of both the data = 2000 + 3575 = 5575
Total number of observations = 80 + 55 = 135
New mean = 5575/135 = 41.3 (nearly)

Answer 2

mean score of whole set= 2090