probability tree
the letters s t a t i s t i c s are random. i pick one letter at random and don't replace it i then randomly pick a second letter draw a tree to represent picking a t and not picking a t
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Oh this is a bit difficult to explain without a white board! Ok so basically at the beginning you're going to have 2 branches, the left hand one with 3/10 along side it and 'T' written at the bottom representing the 3 Ts out of 10 letters and the right hand one with 7/10 written alongside and representing the probability of picking any of the other letters and 'not T' at the bottom of the branch.
Then underneath the 3/10 branch you'll have another 2 branches, the left hand one you will label 2/9 representing the probability of picking a T now that you've already picked one T and only have 9 letters left and you'll write 'T' at the bottom of the branch. The other branch will be labeled 7/9 and have a 'not T' at the bottom of the branch.
Underneath the 7/10 you'll have a left hand branch labeled 3/9 with a 'T' at the bottom other branch labeled 6/9 with 'not T' written at the bottom.
You should finish with a tree with 4 'leaves'.
16 February 2011
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