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In how many $6$ letter permutation of the word "pirayes" ,"r" is some where before "p"?

We should have "r" and "p" for permuting the other letters we have $P^{6}_4$ cases consider that the case is like"iaye" now for "r" we have $5$ cases and we have $6$ cases for "p" and also the cases that "p" is before "r" are equal to the cases that "r" is before "p" so we have $\frac{P^{6}_{4}*5*6}{2}$.The book gave the answer $\frac{P^{6}_{4}*P^{6}_{2}}{2}$ which are equal but I want to know how to get directly the answer $P^{6}_{2}$ when placing "r" and "p" in the rest of the word?

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    You mean the fact that out of the six possible choices two of which have to be "p" and "r", hence $P^6_2$? – 2017-02-23
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    What is a 6 letter permutation of the 8 letter word "pirayesh"? – 2017-02-23
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    @ChristianBlatter means that making a 6 letter word using 6 letters of that word. – 2017-02-23
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    First select one by one $2$ of $6$ **spots**. On the first chosen place letter p and the second chosen letter r. There are $P^6_2$ possibilities. Now select one by one $4$ of the $6$ remaining **letters** and place them from left to right in the open spots. There are $P^6_4$ possibilities. – 2017-02-23

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