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    I have been trying to do this question for ages and just can't get my head around it:
    7. Three letters are selected at random from the 8 letters of the word COMPUTER, without regard to order.
    i) find the number of possiblie selections of 3 letters.
    ii) Find the probability that the letter P is included in the selection.
    Three letters are now selected at random, one at a time, from the 8 letters of the word COMPUTER and placed in order in a line.
    iii) Find the probability that the 3 letters form the word TOP.

    I tried the first one by doing 8C3 which gave me 56.
    I understand in the 2nd question that by choosing P there are only 2 letters you are still choosing. So I tried 8C2 which gave me 28, which is then divided by 56, giving 0.5. I though this probability was far too high.
    On the third one I understand that it is a percolation... and then i though that it was only one event out of the 56. But I am so unsure and really confused.

    Any help would be really appreciated.
    Thanks very much

    Part 2 should be 7C2, as there are only seven letters left once you take out the P.
    As for Part 3, you first need to find out how many permutations of 3 letters you can make from the word, i.e. 8P3.
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Updated: January 22, 2010

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