Maths

The word examination consists of 11 letters -
    (AA), (II), (NN), E, X, M, T, O.
The following combinations are possible:
(a) 2 alike, 2 alike:³C₂ = 3 ways
(b) 2 alike, 2 different:³C₁×⁷C₂ = 63 ways
(c) all 4 different: ⁸C₄ = 70 ways
Hence required number of combinations = 3 +63 +70 = 136.
.
I don't know how the solution has been done. I have just googled the answer and pasted the same here for your reference.

https://www.ilovemaths.com/3combresults.asp