Found problems: 85335
1985 AMC 8, 23
King Middle School has $ 1200$ students. Each student takes $ 5$ classes a day. Each teacher teaches $ 4$ classes. Each class has $ 30$ students and $ 1$ teacher. How many teachers are there at King Middle School?
\[ \textbf{(A)}\ 30 \qquad
\textbf{(B)}\ 32 \qquad
\textbf{(C)}\ 40 \qquad
\textbf{(D)}\ 45 \qquad
\textbf{(E)}\ 50 \qquad
\]
LMT Team Rounds 2010-20, 2020.S12
In the figure above, the large triangle and all four shaded triangles are equilateral. If the areas of triangles $A, B,$ and $C$ are $1, 2,$ and $3,$ respectively, compute the smallest possible integer ratio between the area of the entire triangle to the area of triangle $D.$
[Insert Diagram]
[i]Proposed by Alex Li[/i]
2012 Stanford Mathematics Tournament, 3
Let $ABC$ be an equilateral triangle of side 1. Draw three circles $O_a$, $O_b$, $O_c$ with diameters $BC$, $CA$, and $AB$, respectively. Let $S_a$ denote the area of the region inside $O_a$ and outside of $O_b$ and $O_c$. Define $S_b$ and $S_c$ similarly, and let $S$ be the area of intersection between the three circles. Find $S_a+S_b+S_c-S$.
2005 Purple Comet Problems, 2
We glue together $990$ one inch cubes into a $9$ by $10$ by $11$ inch rectangular solid. Then we paint the outside of the solid. How many of the original $990$ cubes have just one of their sides painted?
2014 IMO Shortlist, C1
Let $n$ points be given inside a rectangle $R$ such that no two of them lie on a line parallel to one of the sides of $R$. The rectangle $R$ is to be dissected into smaller rectangles with sides parallel to the sides of $R$ in such a way that none of these rectangles contains any of the given points in its interior. Prove that we have to dissect $R$ into at least $n + 1$ smaller rectangles.
[i]Proposed by Serbia[/i]
1999 Slovenia National Olympiad, Problem 3
Let $O$ be the circumcenter of a triangle $ABC$, $P$ be the midpoint of $AO$, and $Q$ be the midpoint of $BC$. If $\angle ABC=4\angle OPQ$ and $\angle ACB=6\angle OPQ$, compute $\angle OPQ$.
2023 MOAA, 16
Compute the sum $$\frac{\varphi(50!)}{\varphi(49!)}+ \frac{\varphi(51!)}{\varphi(50!)} + \dots + \frac{\varphi(100!)}{\varphi(99!)}$$ where $\varphi(n)$ returns the number of positive integers less than $n$ that are relatively prime to $n$.
[i]Proposed by Andy Xu[/i]
2018 District Olympiad, 4
Let $ABC$ be a triangle with $\angle A = 80^o$ and $\angle C = 30^o$. Consider the point $M$ inside the triangle $ABC$ so that $\angle MAC= 60^o$ and $\angle MCA = 20^o$. If $N$ is the intersection of the lines $BM$ and $AC$ to show that a $MN$ is the bisector of the angle $\angle AMC$.
Kvant 2022, M2687
We have a regular $n{}$-gon, with $n\geqslant 4$. We consider the arrangements of $n{}$ numbers on its vertices, each of which is equal to 1 or 2. For each such arrangement $K{}$, we find the number of odd sums among all sums of numbers in several consecutive vertices. This number is denoted by $\alpha(K)$.
[list=a]
[*]Find the largest possible value of $\alpha(K)$.
[*]Find the number of arrangements for which $\alpha(K)$ takes this largest possible value.
[/list]
[i]Proposed by P. Kozhevnikov[/i]
2005 AIME Problems, 8
Circles $C_1$ and $C_2$ are externally tangent, and they are both internally tangent to circle $C_3$. The radii of $C_1$ and $C_2$ are $4$ and $10$, respectively, and the centers of the three circles are all collinear. A chord of $C_3$ is also a common external tangent of $C_1$ and $C_2$. Given that the length of the chord is $\frac{m\sqrt{n}}{p}$ where $m,n,$ and $p$ are positive integers, $m$ and $p$ are relatively prime, and $n$ is not divisible by the square of any prime, find $m+n+p$.
2018 Polish MO Finals, 3
Find all real numbers $c$ for which there exists a function $f\colon\mathbb R\rightarrow \mathbb R$ such that for each $x, y\in\mathbb R$ it's true that
$$f(f(x)+f(y))+cxy=f(x+y).$$
Russian TST 2018, P1
The natural numbers $a > b$ are such that $a-b=5b^2-4a^2$. Prove that the number $8b + 1$ is composite.
2011 Rioplatense Mathematical Olympiad, Level 3, 4
We consider $\Gamma_1$ and $\Gamma_2$ two circles that intersect at points $P$ and $Q$ . Let $A , B$ and $C$ be points on the circle $\Gamma_1$ and $D , E$ and $F$ points on the circle $\Gamma_2$ so that the lines $A E$ and $B D$ intersect at $P$ and the lines $A F$ and $C D$ intersect at $Q$. Denote $M$ and $N$ the intersections of lines $A B$ and $D E$ and of lines $A C$ and $D F$ , respectively. Show that $A M D N$ is a parallelogram.
2021 DIME, 13
Let $\triangle ABC$ have side lengths $AB=7$, $BC=8$, and $CA=9$. Let $D$ be the projection from $A$ to $\overline{BC}$ and $D'$ be the reflection of $D$ over the perpendicular bisector of $\overline{BC}$. Let $P$ and $Q$ be distinct points on the line through $D'$ parallel to $\overline{AC}$ such that $\angle APB = \angle AQB = 90^{\circ}$. The value of $AP+AQ$ can be written as $\tfrac{a+b\sqrt{c}}{d}$, where $a$, $b$, $c$, and $d$ are positive integers such that $b$ and $d$ are relatively prime, and $c$ is not divisible by the square of any prime. Find $a+b+c+d$.
[i]Proposed by i3435[/i]
2020 DMO Stage 1, 5.
[b]Q.[/b] Let $ABC$ be a triangle, where $L_A, L_B, L_C$ denote the internal angle bisectors of $\angle BAC, \angle ABC, \angle ACB$ respectively and $\ell_A, \ell_B, \ell_C$, the altitudes from the corresponding vertices. Suppose $ L_A\cap \overline{BC} = \{A_1\}$, $\ell_A \cap \overline{BC} = \{A_2\}$ and the circumcircle of $\triangle AA_1A_2$ meets $AB$ and $AC$ at $S$ and $T$ respectively. If $\overline{ST} \cap \overline{BC} = \{A'\}$, prove that $A',B',C'$ are collinear, where $B'$ and $C'$ are defined in a similar manner.
[i]Proposed by Functional_equation[/i]
2014 Purple Comet Problems, 23
Suppose $x$ is a real number satisfying $x^2-990x+1=(x+1)\sqrt x$. Find $\sqrt x+\tfrac1{\sqrt x}$.
2005 Purple Comet Problems, 24
$\triangle ABC$ has area $240$. Points $X, Y, Z$ lie on sides $AB$, $BC$, and $CA$, respectively. Given that $\frac{AX}{BX} = 3$, $\frac{BY}{CY} = 4$, and $\frac{CZ}{AZ} = 5$, find the area of $\triangle XYZ$.
[asy]
size(175);
defaultpen(linewidth(0.8));
pair A=(0,15),B=(0,-5),C=(25,0.5),X=origin,Y=(4C+B)/5,Z=(5A+C)/6;
draw(A--B--C--cycle^^X--Y--Z--cycle);
label("$A$",A,N);
label("$B$",B,S);
label("$C$",C,E);
label("$X$",X,W);
label("$Y$",Y,S);
label("$Z$",Z,NE);[/asy]
2001 IMC, 4
$p(x)$ is a polynomial of degree $n$ with every coefficient $0 $ or $\pm1$, and $p(x)$ is divisible by $ (x - 1)^k$ for some integer $ k > 0$. $q$ is a prime such that $\frac{q}{\ln q}< \frac{k}{\ln n+1}$. Show that the complex $q$-th roots of unity must be roots of $ p(x). $
2014 JHMMC 7 Contest, 24
When submitting problems, Steven the troll likes to submit silly names rather than his own. On day $1$, he gives no
name at all. Every day after that, he alternately adds $2$ words and $4$ words to his name. For example, on day $4$ he
submits an $8\text{-word}$ name. On day $n$ he submits the $44\text{-word name}$ “Steven the AJ Dennis the DJ Menace the Prince of Tennis the Merchant of Venice the Hygienist the Evil Dentist the Major Premise the AJ Lettuce the Novel’s Preface the Core Essence the Young and the Reckless the Many Tenants the Deep, Dark Crevice”. Compute $n$.
2012 Belarus Team Selection Test, 4
Given $0 < a < b < c$ prove that $$ a^{20}b^{12} + b^{20}c^{12 }+ c^{20}a^{12} <b^{20}a^{12}+ a^{20}c^{12} + c^{20}b^{12} $$
(I. Voronovich)
2003 Italy TST, 3
Let $p(x)$ be a polynomial with integer coefficients and let $n$ be an integer. Suppose that there is a positive integer $k$ for which $f^{(k)}(n) = n$, where $f^{(k)}(x)$ is the polynomial obtained as the composition of $k$ polynomials $f$. Prove that $p(p(n)) = n$.
2003 Junior Balkan Team Selection Tests - Romania, 1
Suppose $ABCD$ and $AEFG$ are rectangles such that the points $B,E,D,G$ are collinear (in this order). Let the lines $BC$ and $GF$ intersect at point $T$ and let the lines $DC$ and $EF$ intersect at point $H$. Prove that points $A, H$ and $T$ are collinear.
2017 Israel National Olympiad, 2
Denote by $P(n)$ the product of the digits of a positive integer $n$. For example, $P(1948)=1\cdot9\cdot4\cdot8=288$.
[list=a]
[*] Evaluate the sum $P(1)+P(2)+\dots+P(2017)$.
[*] Determine the maximum value of $\frac{P(n)}{n}$ where $2017\leq n\leq5777$.
[/list]
1989 IMO Longlists, 28
In a triangle $ ABC$ for which $ 6(a\plus{}b\plus{}c)r^2 \equal{} abc$ holds and where $ r$ denotes the inradius of $ ABC,$ we consider a point M on the inscribed circle and the projections $ D,E, F$ of $ M$ on the sides $ BC\equal{}a, AC\equal{}b,$ and $ AB\equal{}c$ respectively. Let $ S, S_1$ denote the areas of the triangles $ ABC$ and $ DEF$ respectively. Find the maximum and minimum values of the quotient $ \frac{S}{S_1}$
1966 German National Olympiad, 5
Prove that \[\tan 7 30^{\prime }=\sqrt{6}+\sqrt{2}-\sqrt{3}-2.\]