Question 837681
Imagine you are doing what they ask. You
are reaching in the box and picking letters
one at a time.
What they are looking for is the "worst case"
which is the hardest way possible to get SAT.
So imagine this is the order in which you
pull out letters:
M
C
H
U
E
5 letters so far and no S,A, or T
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Now say, the nest letters you get are:
S
S
S
S
That helps, but you only have 1 letter to make SAT
You've got 9 letters so far
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The next letters you get are:
T 
T
11 letters so far, but you're missing the A
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The only letters left in the box are A,A so
the next pick gives you SAT
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That makes 12 letters needed to be CERTAIN that you
have SAT because you know this the the worst
case that can happen