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Nov 2013 p62 q6
2722
The 11 letters of the word REMEMBRANCE are arranged in a line.
Find the number of different arrangements if there are no restrictions.
Find the number of different arrangements which start and finish with the letter M.
Find the number of different arrangements which do not have all 4 vowels (E, E, A, E) next to each other.
Solution
(i) The word REMEMBRANCE has 11 letters with repetitions: 3 E's and 2 M's. The number of different arrangements is given by:
\(\frac{11!}{3! \times 2!} = 1663200\)
(ii) For arrangements starting and ending with M, consider the arrangement as M _ _ _ _ _ _ _ _ M. We arrange the remaining 9 letters (REEMBRANC) with 3 E's:
\(\frac{9!}{3!} = 30240\)
(iii) To find arrangements where the 4 vowels (E, E, A, E) are not together, first calculate the arrangements where they are together. Treat the 4 vowels as a single unit, so we have 8 units to arrange (4 vowels + 7 other letters):