If the mean of 4 observations is 20, when a constant ‘c’ is added to each observation, the mean becomes 22. The value of c is :

A. 6 B. −2 C. 2 D. 4 Answer: Option C
Show Answer Let the four observations are = a, b, d, e $\begin{array}{l}\text{According to the question,}\\ \frac{a+b+e+d}{4}=20\ldots..\text{ (i) }\\ \frac{a+c+b+c+e+c+d+c}{4}=22\\ \frac{4c+(a+b+e+d)}{4}=22\\ \frac{4c}{4}+20=22\\ c=2\end{array}$