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June 2016 p62 q7
2710
Find the number of different arrangements which can be made of all 10 letters of the word WALLFLOWER if
there are no restrictions,
there are exactly six letters between the two Ws.
Solution
(i) The word WALLFLOWER consists of 10 letters where L is repeated twice. The number of different arrangements is given by:
\(\frac{10!}{2!} = \frac{3628800}{2} = 302400\)
(ii) To have exactly six letters between the two Ws, consider the positions of the Ws as fixed with six letters in between them. The remaining 8 letters (including the two Ls) can be arranged in the remaining positions. The number of ways to arrange these 8 letters is:
\(\frac{8!}{2!} = \frac{40320}{2} = 20160\)
Since there are three possible positions for the Ws (e.g., W******W*, **W******W, W******W**), we multiply by 3: