Question

If the mean of 25 observations is 27 and each is decreased by 7. What will be the new mean?

Answer 1

mean of 25 observations =27

sum of 25 observations =27×25=675

subtracted 7 from each =25×7=175

so,sum of 25 observations-175=675-175
sum of 25 observations-175=500
mean of 25 observations =500÷25=20
ANS:- 20

Answer 2

Mean=sum of observations/number of observations

27=sum of obs./25

27*25=sum of obs

Sum of all obs=675

Let the obs which us added be equal to x

So the mean remains the same(given)

27=(675+x)/26

27*26=675+x

702-675=x

27=x

The observation which when added to the data keeps the mean unchanged is 27

The new no. of observations will be 26 and the total of all observations will be 27