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 :

Answer: Option C

Let the four observations are = a, b, d, e
According to the question,
$$\frac{a+b+e+d}{4}$$   = 20.....(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