Chapter 8: Problem 1
Determine how many \(n \in \mathbf{Z}^{+}\)satisfy \(n \leq 500\) and are not divisible by \(2,3,5,6,8\), or 10 .
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Chapter 8: Problem 1
Determine how many \(n \in \mathbf{Z}^{+}\)satisfy \(n \leq 500\) and are not divisible by \(2,3,5,6,8\), or 10 .
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Give a combinatorial argument to verify that for all \(n \in \mathbf{Z}^{+}\), $$ n !=\left(\begin{array}{l} n \\ 0 \end{array}\right) d_{0}+\left(\begin{array}{l} n \\ 1 \end{array}\right) d_{1}+\left(\begin{array}{l} n \\ 2 \end{array}\right) d_{2}+\cdots+\left(\begin{array}{l} n \\ n \end{array}\right) d_{n}=\sum_{k=0}^{n}\left(\begin{array}{l} n \\ k \end{array}\right) d_{k} $$ (For each \(1 \leq k \leq n, d_{k}=\) the number of derangements of 1 \(2,3, \ldots, k ; d_{0}=1 .\) )
Determine the number of positive integers \(n, 1 \leq n \leq 2000\), that are a) not divisible by 2,3 , or 5 b) not divisible by \(2,3,5\), or 7 c) not divisible by 2,3 , or 5 , but are divisible by 7
a) Let \(A=\\{1,2,3, \ldots, 7\\}\). A function \(f: A \rightarrow A\) is said to have a fixed point if for some \(x \in A, f(x)=x\). How many one-to-one functions \(f: A \rightarrow A\) have at least one fixed point? b) In how many ways can we devise a secret code by assigning to each letter of the alphabet a different letter to represent it?
In how many ways can one arrange the letters in CORRESPONDENTS so that (a) there is no pair of consecutive identical letters? (b) there are exactly two pairs of consecutive identical letters? (c) there are at least three pairs of consecutive identical letters?
a) In how many ways can the letters in ARRANGEMENT be arranged so that there are exactly two pairs of consecutive identical letters? at least two pairs of consecutive identical letters? b) Answer part (a), replacing two with three.
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