Chapter 7: Problem 3
A small town has only 500 residents. Must there be 2 residents who have the same birthday? Why?
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These are the key concepts you need to understand to accurately answer the question.
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Chapter 7: Problem 3
A small town has only 500 residents. Must there be 2 residents who have the same birthday? Why?
These are the key concepts you need to understand to accurately answer the question.
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Suppose six pairs of similar-looking boots are thrown together in a pile. How many individual boots must you pick to be sure of getting a matched pair? Why?
How many integers from 1 through 100 must you pick in order to be sure of getting one that is divisible by 5 ?
Exercises \(40-47\) refer to the following definition: Definition: If \(f: X \rightarrow Y\) is a function and \(A \subseteq X\) and \(C \subseteq Y\) then $$ f(A)=\\{y \in Y \mid y=f(x) \text { for some } x \text { in } A\\} $$ and $$ f^{-1}(C)=\\{x \in X \mid f(x) \in C\\} $$ Determine which of the properties in \(40-47\) are true for all functions \(f\) from a set \(X\) to a set \(Y\) and which are false for some function \(f\). Justify your answers. For all subsets \(A\) and \(B\) of \(X\), if \(A \subseteq B\), then \(f(A) \subseteq f(B)\).
Suppose \(X\) and \(Y\) are finite sets, \(X\) has more elements than \(Y\), and \(F: X \rightarrow Y\) is a function. By the pigeonhole principle, there exist elements \(a\) and \(b\) in \(X\) such that \(a \neq b\) and \(F(a)=F(b)\). Write a computer algorithm to find such a pair of elements \(a\) and \(b\). "James E. Schultz and William F. Burger, "An Approach to Problem-Solving Using Equivalence Classes Modulo \(n, "\) College Mathematics Journal (15), No. \(5,1984,401-405\).
a. Suppose \(a_{1}, a_{2} \ldots \ldots, a_{n}\) is a sequence of \(n\) integers none of which is divisible by \(n\). Show that at least one of the differences \(a_{i}-a_{j}\) (for \(i \neq j\) ) must be divisible by \(n\). \(\boldsymbol{H}\) b. Show that every finite sequence \(x_{1}, x_{2}, \ldots, x_{n}\) of \(n\) integers has a consecutive subsequence \(x_{l+1}, x_{i+2}, \ldots, x_{j}\) whose sum is divisible by \(n\). (For instance, the sequence \(3,4,17,7,16\) has the consecutive subsequence \(17,7,16\) whose sum is divisible by \(5 .)^{*}\)
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