Since we know, Permutation of n objects taking r at a time is ⁿP_r,and permutation of n objects taking all at a time is n!

And, we also know Permutation of n objects taking all at a time having p objects of the same type, q objects of another type, r objects of another type is . i.e. the, number of repeated objects of same type are in denominator multiplication with factorial.

Given, the word SERIES. It has 6 letters, and it has 2 repeated letter ‘S,’ and ‘E.’ The letter S is repeated twice, and letter E is also repeated twice. And all other letters are distinct.

The problem can now be rephrased as to find a total number of permutations of 6 objects (S, E, R, I, E, S) of which two objects are of same type (S, S), and two objects are of another type (E, E).

Total number of such permutations

= 180

Hence, a total number of permutations of the word SERIES is 180.