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Search results for combinatorics

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2
Set system and linear algebra
We have $m$ sets $A_1,A_2,A_3 \text{ to } A_m$. All $A_i \subseteq [n]$ where $ [n] = \{1,2,3, \dots n \}.$ Given that $|A_i| = \text{odd number}$ and $|A_i \cap A_j| = \text{even number }\forall i \neq j$. Show that $m \leq n$.
We have $m$ sets $A_1,A_2,A_3 \text{ to } A_m$. All $A_i \subseteq [n]$ where $ [n] = \{1,2,3, \dots n \}.$ Given that $|A_i| = \text{odd number}$ and $|A_i \cap A_j| = ...
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1 answer
3
Induction
Prove that the number of edges in a graph with exactly one triangle is at most \begin{align*} \frac{\left( n - 1 \right )^2}{4} + 2 \end{align*}
Prove that the number of edges in a graph with exactly one triangle is at most \begin{align*} \frac{\left( n - 1 \right )^2}{4} + 2\end{align*}
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4
Set theory
Consider the sets $A_1, A_2, A_3 \dots A_m$. Prove that the number of distinct sets of the form $A_i \oplus A_j$ is at least $m$.
Consider the sets $A_1, A_2, A_3 \dots A_m$. Prove that the number of distinct sets of the form $A_i \oplus A_j$ is at least $m$.
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5
Probability and random variable
Consider the sets $A_1, A_2, A_3 \dots A_m$ each a subset of size $k$ of $\{1,2,3, \dots , n\}$. If in a 2-colouring of $\{1,2,3, \dots , n\}$ no set $A_i$ is monochromatic, then show that $ m < 2^{k-1}$.
Consider the sets $A_1, A_2, A_3 \dots A_m$ each a subset of size $k$ of $\{1,2,3, \dots , n\}$. If in a 2-colouring of $\{1,2,3, \dots , n\}$ no set $A_i$ is monoch...
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8
Probability
Prove for a positive integer valued random variable, $X$ , and for positive integers $a < b$ \begin{align*} &P(X \geq b) \leq \left [ \left ( \frac{E(X)}{b} \right ) - P(a \leq X < b)\cdot \left ( \frac{a}{b} \right ) \right ] \\ \end{align*}
Prove for a positive integer valued random variable, $X$ , and for positive integers $a < b$\begin{align*} &P(X \geq b) \leq \left [ \left ( \frac{E(X)}{b} \right ) - P(...
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