Question

mean of 12 observation is 17 if each observation is decreased by 2 find new mean

Answer 1

Solution:-

Mean of 12 observations = 17
Sum of 12 observations = 12*17
= 204
Given : If each observation is decreased by 2
Then, the sum of 12 observations = 204 - (12*2)
= 204 - 24
= 180
Now, 
New mean of 12 observations = 180/12
= 15 
Answer.

Answer 2

Mean=Sum of terms/number of terms
17=Sum of terms/12
Sum of terms=17*12=204
Now by decreasing each term by 2 from 12 terms sum will be decreased by 24 now Sum of terms=204-24=180
So new mean will be
Mean=180/12=15