6:40 The mean and the variance of a group of 100 observations are 6.5 and 3.0 respectively. 55 of these observations have mean 6.6 and standard deviation 1.5. Find the mean and the S.D. of the remaining 45 observations. 6:40 The mean and the variance of a group of 100 observations are 6.5 and 3.0 respectively. 55 of these observations have mean 6.6 and standard deviation 1.5. Find the mean and the S.D. of the remaining 45 observations