Question

write ten words using the letters of the word given below . No words must be written have fewer words than 4 letter . No letter must be written twice in the same words except for 'I' and 'E'. word : OBIDIENCE
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Answer 1

Answer:

The number of permutations if all letters were distinct = 6P3.

As 'S' and 'E' are repeating, the arrangement in which 'S' are interchanged are the same, so we divide by 2! for 'S' and likewise for 'E'.

Number of permutations =6P32!.2!=30

Which isn't the correct answer. I would like to get some help here.