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Specialist Mathematics · Unit 1 · Combinatorics · Permutations (ordered arrangements) and combinations (unordered selections)

Use factorial notation.

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Question 1

Simplify $\frac{8!}{6!}$.

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Question 2

Consider the expression $\frac{(n+2)!}{n!}$ where $n$ is a positive integer. (a) Use factorial notation to simplify this expression. (1 mark) (b) Hence determine the value of the expression when $n = 8$. (1 mark) (c) Use your result from part (a) to solve the equation $\frac{(k+2)!}{k!} = 132$ for positive integer $k$. (1 mark)

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Question 3

The table below shows values of a function $f(n)$ for selected positive integers $n$. Given that $f(n) = \frac{k \cdot (3n)!}{n! \cdot (2n)!}$ for some constant $k \in \mathbb{Z}^+$, determine the value of $k$, and hence evaluate $f(8)$.

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Question 4

Use factorial notation to express the product $7 \times 6 \times 5 \times 4$.

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Question 5

Determine the value of $n$ that satisfies the equation $\frac{(n+2)!}{n!} - \frac{(n+1)!}{(n-1)!} = 56$.

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Use the notation (𝑛 𝑟) and 𝐶𝑟 𝑛 to represent the number of ways of selecting 𝑟 objects from 𝑛 distinct objects where order is not important. 𝐶𝑟 𝑛 = (𝑛 𝑟) = 𝑛! 𝑟!(𝑛−𝑟)!
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