Math: Counting Principles and Probability CONFUSION MY GOODNES

DrSteve
Thu, 02 Jan 2014 04:01:26 +0000

Your mistake is that you should be using a combination and not a permutation. You are counting the total number of ways to choose 2 angles from 4. Once you choose these 2 angles you are NOT arranging them. For example, choosing angle 1 and angle 2 is the same thing as choosing angle 2 and angle 1. So for the denominator simply type 4C2 in your calculator.

It’s also very quick to count these pairs by hand (as I think you’ve noticed).

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