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
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OCR s1 june 2009 watch
- Thread Starter
- 22-01-2010 19:46
- 22-01-2010 21:26
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.