⇒ sum of observations = (18)(- 7) = - 126 Now, each observation is increased by 3. ⇒ sum of observations of new set = -126 + (3)(18) = - 72 Mean of new set =
sum of observation of new set
no. of observations of new set
⇒ Mean of new set =
−72
18
⇒ Mean of new set =−4 Hence, the mean of 18 observation is -7 and if each observation is increased by 3, the mean of the new set is - 4