The mean of the series x1,x2,…,xn is X¯. If x2 is replaced by λ, then the new mean is
X¯−x2+λ
X¯−x2−λn
(n−1)X¯+λn
nX-x2+λn
We have,
X¯=x1+x2+…+xn−1+xnn⇒ nX¯=x1+x2+…+xn−1+xn
new mean=nX-x2+λn