UPSC NDA Math Model Paper 2

Given, The mean of 18 observation is -7
Mean =

sum of observation

no. of observations

⇒−7=

sum of observation

18

⇒ 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