How many 4 letters words can be formed using the letters of the words '`INEFFECTIVE`'

Explanation

Number of repeated words :

1 times=N,C,T,V

2 times=I,F

3 times=E


= {all 4 letters different} + {2 same ,1 different,1 different letters} + {2 same ,2 same letters} + {3 same,1 different letters}


=`^7P_4+3^C_1xx.^6C_2xx(4!)/(2!)+.^3P_2xx(4!)/(2!2!)+.^1C_1xx.^6C_1xx(4!/3!)`

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