The Greatest Combinatorics

In how many ways can the letters of the word AGREATESTMATH be arranged so that no 2 vowels are together?


The answer is 8467200.

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1 solution

Ashish Menon
Dec 30, 2016

AGREATESTMATH contains 13 letters of which 8 are consonants and 5 vowels. First lets arrange the consonants by 8 ! 3 ! \dfrac{8!}{3!} (T repeats 3 times). Now, there are (8 + 1 = 9) places amde by these 8 consonants.And we have to arrange 5 vowels in them. Now, choose 5 places by ( 9 5 ) \dbinom{9}{5} . Now, arrange them by 5 ! 2 ! × 3 ! \dfrac{5!}{2! × 3!} (A repeats thrice and E repeats twice). So, our final answer is 8 ! 3 ! × ( 9 5 ) × 5 ! 2 ! × 3 ! = 8467200 \dfrac{8!}{3!} × \dbinom{9}{5} × \dfrac{5!}{2! × 3!} = \color{#3D99F6}{\boxed{8467200}} .

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