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If the letters of the word REGULATIONS bearranged at random, find the probability that there will be exactly fourletters between the `R`and the`Edot` |
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Answer» Correct Answer - `(11!)/(.^(9)P_(4)xx6! xx 2!)` Total number of ways of arranging 11 letters is (11)! The number of selection of 4 letters to be placed between R and E from remaining 9 is `.^(9)C_(4)`. These four letters can be permuted in 4! Ways. Now R and E can be interchanged in 2! Ways. `underset("4 letter")ubrace((R....))underset(" 5 letter")ubrace(E")".....)` Hence, the number of favorable ways is `.^(9)C_(4) xx 4! xx 6! xx 2!` Therefore, the required probability is `(11!)/(.^(9)P_(4) xx 6! xx2!)` |
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