Question

The mean of 21 numbers is 15. If each number is multiplied by 2, what will be the new mean and hence state the relation between the new mean and the old mean.

Answer 1

let
x/21=15=M(old) .............................(1)
when each number is multiplied by 2
then
2{x/21}=M(new) .................................(2)

from eq 1
M(old)=2*15=30

then
relation is
M(old)=2M(new)

Answer 2

Mean of 21 numbers = 15

Given that each number is multiplied by 2, then Mean = ?

We know that if all the observations are multiplied by a given number then simply their mean is multiplied by 2 to obtain the new mean.

Hence,

New mean = 2 * Old Mean
OR New mean = 2 * 15
OR New mean = 30

Now,

The relation between the new mean and old mean is as follows:

New Mean = 2 * Old Mean