Found problems: 85335
2011 VJIMC, Problem 4
Let $a,b,c$ be elements of finite order in some group. Prove that if $a^{-1}ba=b^2$, $b^{-2}cb^2=c^2$, and $c^{-3}ac^3=a^2$ then $a=b=c=e$, where $e$ is the unit element.
2002 Tournament Of Towns, 4
The spectators are seated in a row with no empty places. Each is in a seat which does not match the spectator's ticket. An usher can order two spectators in adjacent seats to trade places unless one of them is already seated correctly. Is it true that from any initial arrangement, the spectators can be brought to their correct seats?
2021 China Second Round Olympiad, Problem 2
Compute the value of $$\sin^2 20^{\circ} + \cos^2 50^{\circ} + \sin 20^{\circ} \cos 50^{\circ}.$$
[i](Source: China National High School Mathematics League 2021, Zhejiang Province, Problem 2)[/i]
2016 LMT, 7
Compute the product of the three smallest prime factors of
\[21!\cdot 14!+21!\cdot 21+14!\cdot 14+21\cdot 14.\]
[i]Proposed by Daniel Liu
2006 Tournament of Towns, 2
When Ann meets new people, she tries to find out who is acquainted with who. In order to memorize it she draws a circle in which each person is depicted by a chord; moreover, chords corresponding to acquainted persons intersect (possibly at the ends), while the chords corresponding to non-acquainted persons do not. Ann believes that such set of chords exists for any company. Is her judgement correct? (5)
2024 LMT Fall, 3
Jason starts in a cell of the grid below. Every second he moves to an adjacent cell (i.e., two cells that share a side) that he has not visited yet. Find the maximum possible number of cells that Jason can visit.
[asy]
size(3cm);
draw((1,0)--(4,0));
draw((0,1)--(5,1));
draw((0,2)--(5,2));
draw((0,3)--(5,3));
draw((0,4)--(5,4));
draw((1,5)--(4,5));
draw((0,1)--(0,4));
draw((1,0)--(1,5));
draw((2,0)--(2,5));
draw((3,0)--(3,5));
draw((4,0)--(4,5));
draw((5,1)--(5,4));
[/asy]
1998 National Olympiad First Round, 29
Let $ ABCD$ be convex quadrilateral with $ \angle C\equal{}\angle D\equal{}90{}^\circ$. The circle $ K$ passing through $ A$ and $ B$ is tangent to $ CD$ at $ C$. Let $ E$ be the intersection of $ K$ and $ \left[AD\right]$. If $ \left|BC\right|\equal{}20$, $ \left|AD\right|\equal{}16$, then $ \left|CE\right|$ is
$\textbf{(A)}\ 9 \qquad\textbf{(B)}\ 6\sqrt{2} \qquad\textbf{(C)}\ 4\sqrt{5} \qquad\textbf{(D)}\ 7\sqrt{2} \qquad\textbf{(E)}\ 10$
1976 AMC 12/AHSME, 8
A point in the plane, both of whose rectangular coordinates are integers with absolute values less than or equal to four, is chosen at random, with all such points having an equal probability of being chosen. What is the probability that the distance from the point to the origin is at most two units?
$\textbf{(A) }\frac{13}{81}\qquad\textbf{(B) }\frac{15}{81}\qquad\textbf{(C) }\frac{13}{64}\qquad\textbf{(D) }\frac{\pi}{16}\qquad \textbf{(E) }\text{the square of a rational number}$
1991 French Mathematical Olympiad, Problem 2
For each $n\in\mathbb N$, the function $f_n$ is defined on real numbers $x\ge n$ by
$$f_n(x)=\sqrt{x-n}+\sqrt{x-n+1}+\ldots+\sqrt{x+n}-(2n+1)\sqrt x.$$(a) If $n$ is fixed, prove that $\lim_{x\to+\infty}f_n(x)=0$.
(b) Find the limit of $f_n(n)$ as $n\to+\infty$.
2017 Denmark MO - Mohr Contest, 1
A system of equations
$$\begin{cases} x^2 \,\, ? \,\, z^2 = -8 \\ y^2 \,\, ? \,\, z^2 = 7 \end{cases}$$
is written on a piece of paper, but unfortunately two of the symbols are a little blurred. However, it is known that the system has at least one solution, and that each of the two question marks stands for either $+$ or $-$. What are the two symbols?
2023 CIIM, 2
A toymaker has $k$ dice at his disposal, each with $6$ blank sides. On each side of each of these dice, the toymaker must draw one of the digits $0, 1, 2, \ldots , 9$.
Determine (in terms of $k$) the largest integer $n$ such that the toymaker can draw digits on the $k$ dice such that, for any positive integer $r \leq n$, it is possible to choose some of the $k$ dice and form with them the decimal representation of $r$.
[b]Note:[/b] The digits 6 and 9 are distinguishable: they appear as [u]6[/u] and [u]9[/u].
2022 Francophone Mathematical Olympiad, 2
We consider an $n \times n$ table, with $n\ge1$. Aya wishes to color $k$ cells of this table so that that there is a unique way to place $n$ tokens on colored squares without two tokens are not in the same row or column. What is the maximum value of $k$ for which Aya's wish is achievable?
1970 Miklós Schweitzer, 12
Let $ \vartheta_1,...,\vartheta_n$ be independent, uniformly distributed, random variables in the unit interval $ [0,1]$. Define \[ h(x)\equal{} \frac1n \# \{k: \; \vartheta_k<x\ \}.\] Prove that the probability that there is an $ x_0 \in (0,1)$ such that $ h(x_0)\equal{}x_0$, is equal to $ 1\minus{} \frac1n.$
[i]G. Tusnady[/i]
2010 Germany Team Selection Test, 3
Let $f$ be any function that maps the set of real numbers into the set of real numbers. Prove that there exist real numbers $x$ and $y$ such that \[f\left(x-f(y)\right)>yf(x)+x\]
[i]Proposed by Igor Voronovich, Belarus[/i]
1996 AMC 8, 11
Let $x$ be the number
\[0.\underbrace{0000...0000}_{1996\text{ zeros}}1,\]
where there are 1996 zeros after the decimal point. Which of the following expressions represents the largest number?
$\text{(A)}\ 3+x \qquad \text{(B)}\ 3-x \qquad \text{(C)}\ 3\cdot x \qquad \text{(D)}\ 3/x \qquad \text{(E)}\ x/3$
2012 Dutch BxMO/EGMO TST, 2
Let $\triangle ABC$ be a triangle and let $X$ be a point in the interior of the triangle. The second intersection points of the lines $XA,XB$ and $XC$ with the circumcircle of $\triangle ABC$ are $P,Q$ and $R$. Let $U$ be a point on the ray $XP$ (these are the points on the line $XP$ such that $P$ and $U$ lie on the same side of $X$). The line through $U$ parallel to $AB$ intersects $BQ$ in $V$ . The line through $U$ parallel to $AC$ intersects $CR$ in $W$. Prove that $Q, R, V$ , and $W$ lie on a circle.
2003 CHKMO, 2
In conference there $n>2$ mathematicians. Every two mathematicians communicate in one of the $n$ offical languages of the conference. For any three different offical languages the exists three mathematicians who communicate with each other in these three languages. Find all $n$ such that this is possible.
2019 BMT Spring, 10
Let $MATH$ be a square with $MA = 1$. Point $B$ lies on $AT$ such that $\angle MBT = 3.5 \angle BMT$. What is the area of $\vartriangle BMT$?
2008 Bundeswettbewerb Mathematik, 2
Let the positive integers $ a,b,c$ chosen such that the quotients $ \frac{bc}{b\plus{}c},$ $ \frac{ca}{c\plus{}a}$ and $ \frac{ab}{a\plus{}b}$ are integers. Prove that $ a,b,c$ have a common divisor greater than 1.
2013 Czech And Slovak Olympiad IIIA, 1
Find all pairs of integers $a, b$ for which equality holds $\frac{a^2+1}{2b^2-3}=\frac{a-1}{2b-1}$
1960 Polish MO Finals, 2
A plane is drawn through the height of a regular tetrahedron, which intersects the planes of the lateral faces along $ 3 $ lines that form angles $ \alpha $, $ \beta $, $ \gamma $ with the plane of the tetrahedron's base. Prove that
$$ tg^2 \alpha + tg^2 \beta + tg^2 \gamma =12.$$
2021 All-Russian Olympiad, 7
Find all permutations $(a_1, a_2,...,a_{2021})$ of $(1,2,...,2021)$, such that for every two positive integers $m$ and $n$ with difference bigger than $20^{21}$, the following inequality holds:
$GCD(m+1, n+a_1)+GCD(m+2, n+a_2)+...+GCD(m+2021, n+a_{2021})<2|m-n|$.
Russian TST 2018, P1
Let $ABC$ be an isosceles triangle with $AB = AC$. Let P be a point in the interior of $ABC$ such that $PB > PC$ and $\angle PBA = \angle PCB$. Let $M$ be the midpoint of the side $BC$. Let $O$ be the circumcenter of the triangle $APM$. Prove that $\angle OAC=2 \angle BPM$ .
2018 Mediterranean Mathematics OIympiad, 3
An integer $a\ge1$ is called [i]Aegean[/i], if none of the numbers $a^{n+2}+3a^n+1$ with $n\ge1$ is prime.
Prove that there are at least 500 Aegean integers in the set $\{1,2,\ldots,2018\}$.
(Proposed by Gerhard Woeginger, Austria)
2013 India PRMO, 10
Carol was given three numbers and was asked to add the largest of the three to the product of the other two. Instead, she multiplied the largest with the sum of the other two, but still got the right answer. What is the sum of the three numbers?