The skill being taught is how to calculate the values of combinations, specifically "N choose M". This process involves using factorials to determine the number of combinations by dividing the factorial of N by the product of the factorial of M and the factorial of (N-M).
Calculating values of N choose M, including with multiplication and division
Test your understanding of calculating combinations by practicing it! Work through the below exercises to use it in practice.
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What is the value of this probability expression?
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First let's change it from binomial form so it might be a little easier to talk about.
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Now we can start tackling one term at a time. Let's start on the top with 4 choose 2. That's 4 factorial, over 2 factorial, multiplied by, 4 minus 2 factorial
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Calculating that term, its value is 6, so we can plug that in.
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Now let's move to the bottom and tackle 2 choose 2. That's 2 factorial, over 2 factorial, multiplied by, 2 minus 2 factorial
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Since both zero and one, factorial, are just 1, our value is 1, so we can plug that in.
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Now our final term is 3 choose 2. That's 3 factorial, over 2 factorial, multiplied by, 3 minus 2 factorial
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Which has a value of 3
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With all terms calculated, we can see that our expression's value is 2