Question: The mean of n observations is $ {{\bar{x}}_1}. $ If the first observation is increased by 1, second by 2 and so on, then their mean is $ {{\bar{x}}_2}. $ The value of $ {{\bar{x}}_2}-{{\bar{x}}_1} $ is [Oriental Insurance Company (AAO) 2012]
Options:
A) $ n $
B) $ \frac{n}{2}+1 $
C) $ \frac{n(n+1)}{2} $
D) $ \frac{(n+1)}{2} $
E) None of these
Show Answer
Answer:
Correct Answer: D
Solution:
- Here, new mean, $ {{\bar{x}}_2} $
$ =\frac{x _1+x _2+…+x _{n}}{n}+\frac{1+2+3+…+n}{n} $
$ ={{\bar{x}}_1}+\frac{n(n+1)}{2n}={{\bar{x}}_1}=\frac{n+1}{2} $
$ \therefore $ $ {{\bar{x}}_2}+{{\bar{x}}_1}={{\bar{x}}_1}+\frac{n+1}{2}-{{\bar{x}}_1}=\frac{n+1}{2} $