UPSC NDA Math Model Paper 7

Given: Mean of seven numbers is 8
Here n = 10,
Let seven numbers be x1,x2,x3,......,x7
Mean =

∑xi

n

=

x1+x2+x3+.....+x7

7

=8
⇒x1+x2+x3+.....+x7=56
Now, A new number 16 is added.
Mean of eight numbers =

∑xi

n

=

x1+x2+x3+.....+x7+16

8

From equation (1) we get
Mean of eight numbers =

56+16

8

=

72

8

=9