How many permutations are there of all the letters of the word PATHFINDER with the following restrictions: 1) no vowels together, 2) all vowels together. I know there are 10! ways to arrange 10 different letters. Not sure how to address the restriction of no vowels together. In case 2, all vowels together, means the three vowels are a group. They can appear at the beginning, the end, or in the 6 spaces in between the 7 consonants. I'm not sure how to set up the calculation….help would be appreciated.
How many permutations are there of all the letters of the word PATHFINDER with restrictions…
permutations
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Best Answer
For all the vowels together, as pointed out in comments, the AIE can be treated as a "letter" with $3!=6$ variations. Then there are $8!$ permutations of the "letters", yielding $6×8!=241920$ permutations in all.
The calculation when none of the vowels together involves stars and bars, where three vowels need to be placed in the $8$ spaces between and around the consonants. This yields $\binom83$ arrangements of consonants and vowels, and for each arrangement the vowels and consonants can be permuted in $3!×7!$ ways, giving $\binom83×3!×7!=1693440$ valid permutations.