total permutations =
No. of permutations containing ‘H I N’ = 7!
No. of permutations containing ‘D U S’ =
No. of permutations containing ‘T A N’ =7!
No. of permutations containing ‘H I N’ and ‘D U S’ = 5 !
No. of permutations containing ‘D U S’ and ‘T A N’ = 5 !
No. of permutations containing ‘T A N’ and ‘H I N’ = 5 !
No. of permutations containing ‘H I N’, ‘D U S’ and ‘T A N’ = 3 !
∴ Required permutations =
- [7! +
+ 7! - 5! - 5! - 5! + 3!]
= 169194