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June 2023 p51 q3
2705
(a) Find the number of different arrangements of the 8 letters in the word COCOONED.
(b) Find the number of different arrangements of the 8 letters in the word COCOONED in which the first letter is O and the last letter is N.
(c) Find the probability that a randomly chosen arrangement of the 8 letters in the word COCOONED has all three Os together given that the two Cs are next to each other.
Solution
(a) The word COCOONED has 8 letters with repetitions: 2 Cs, 3 Os. The number of different arrangements is given by:
\(\frac{8!}{2!3!} = 3360\)
(b) Fixing the first letter as O and the last letter as N, we arrange the remaining 6 letters: C, C, O, O, E. The number of arrangements is:
\(\frac{6!}{2!2!} = 180\)
(c) Treat the three Os as a single unit and the two Cs as another unit. We have the units: OOO, CC, E, N, D. The number of arrangements of these 5 units is:
\(\frac{5!}{1!} = 120\)
The number of arrangements where the two Cs are together is: