You have the numbers 1-24 written on slips of paper. If you choose one slip at random, what is the probability that you will not select a number which is divisible by 3?

1 Answer
MathFact-orials.blogspot.com
Sep 26, 2016

#2/3#

Explanation:

We can look at this a few ways. Let me show you mine:

24 is divisible by 3, but 23 and 22 are not.
21 is divisible by 3, but 20 and 19 are not.
18 is divisible by 3, but...
15 is divisible by 3, but...
12 is divisible by 3, but...
9 is divisible by 3, but...
6 is divisible by 3, but...
3 is divisible by 3, but...

(Sorry - got lazy writing all that out...)

In each group of three, one is divisible by 3 and two are not. So the odds of picking one that is divisible by 3 is #1/3# and of not is #2/3#.

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