Q6Short answer
The mean and standard deviation of some data for the time taken to complete a test are calculated with the following results: Number of observations = 25, mean = 18.2 seconds, standard deviation = 3.25 seconds. Further, another set of 15 observations x1, x2, ..., x15, also in seconds, is now 15 15 available and we have ∑ xi = 279 and ∑ xi = 5524 . Calculate the standard i =1 i =1 derivation based on all 40 observations.