Unformatted text preview: r).
I have seen some very good shortcuts for solving this question (and others like it). But I would like to offer
you a fast and foolproof method. My method is probability based and I call it "A probability approach for
solving counting problems" method.
Now let Y be the ... don't worry! No Y is needed, just wanted to sound smart! (And as you know every good
math/physics/finance paper starts with "let something be something")
So I would like to start with a simple problem, very simple problem:
How many integers from 1 to 100 including, has a units digit of 5?
A) 5
B) 9
C) 10
D) 11
E) 20
This is a 350 level question; all you need to do is to list the integers that has 5 as the units digit, I call this
the basic method, meaning Count(5,15,25,35,45,55,65,75,85,95) = 10. The answer is (C).
Using the probability method we can see we have two places for digit in the integer XX and we need to fill in
the tens di...
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 Fall '13
 Numerical digit, digit, 4digit, 4 digits, probability method

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