Mean of 3 numbers = 10
Mean of 4 numbers = 12
Mean = Sum of observations/ Number of observations
10 = Sum of 3 observations/3
⇒ Sum of 3 observations = 30 ........ (1)
and 12 = Sum of 4 observations/4
⇒ Sum of 4 observations = 48 ........ (2)
From (1) and (2), we get
Sum of 7 observations = 30 + 48 = 78
Required mean = Sum of 7 observations/7
= 78/7
= 11.14
