Found problems: 85335
Compute the smallest positive integer that gives a remainder of $1$ when divided by $11$, a remainder of $2$ when divided by $21$, and a remainder of $5$ when divided by $51$.
[i]2021 CCA Math Bonanza Lightning Round #3.3[/i]
Consider an acute-angled triangle $ABC$ with $AB=AC$ and $\angle A>60^\circ$. Let $O$ be the circumcenter of $ABC$. Point $P$ lies on circumcircle of $BOC$ such that $BP\parallel AC$ and point $K$ lies on segment $AP$ such that $BK=BC$. Prove that $CK$ bisects the arc $BC$ of circumcircle of $BOC$.
Given pairwise coprime natural numbers $ x $, $ y $, $ z $, $ t $ such that $ xy + yz + zt = xt $. Prove that the sum of the squares of some two of these numbers is twice the sum of the squares of the two remaining.
Solve the equation
\[\int_0^1(x+y)^2u(x)dx=\lambda u(y)+1\]
Solve the equation $4xy-x-y=z^2$ in positive integers.
A square is divided into $16$ equal squares, obtaining the set of $25$ different vertices. What is the least number of vertices one must remove from this set, so that no $4$ points of the remaining set are the vertices of any square with sides parallel to the sides of the initial square?
Let $k$ be a natural number.Find all the couples of natural numbers $(n,m)$ such that :
$(2^k)!=2^n*m$
The number $6545$ can be written as a product of a pair of positive two-digit numbers. What is the sum of this pair of numbers?
$\text{(A)}\ 162 \qquad \text{(B)}\ 172 \qquad \text{(C)}\ 173 \qquad \text{(D)}\ 174 \qquad \text{(E)}\ 222$
Given a right triangle $ABC$ with $ \angle C=90^o$. On its hypotenuse $AB$ is arbitrary mark the point$ P$. The point $Q$ is symmetric to the point $P$ wrt $AC$. Let the lines $PQ$ and $BQ$ intersect $AC$ at points $O$ and $R$ respectively. Denote by $S$ the foot of the perpendicular from the point $R$ on the line $AB$ ($S \ne P$), and let $T$ be the intersection point of lines $OS$ and $BR$. Prove that $R$ is the center of the circle inscribed in the triangle $CST$.
In an $m\times n$ rectangular grid, where m and n are odd integers, $1\times 2$ dominoes are initially placed so as to exactly cover all but one of the $1\times 1$ squares at one corner of the grid.
It is permitted to slide a domino towards the empty square, thus exposing another square.
Show that by a sequence of such moves, we can move the empty square to any corner of the rectangle.
[i]A. Shapovalov[/i]
Show that for each positive integer $n,$ all the roots of the polynomial \[\sum_{k=0}^n 2^{k(n-k)}x^k\] are real numbers.
For $n \ge 1$ call a finite sequence $(a_1, a_2 \ldots a_n)$ of positive integers [i]progressive[/i] if $a_i < a_{i+1}$ and $a_i$ divides $a_{i+1}$ for all $1 \le i \le n-1$. Find the number of progressive sequences such that the sum of the terms in the sequence is equal to $360$.
Let $S_{n}$ be the number of permutations $(a_{1}, a_{2}, ... , a_{n})$ of $(1, 2, ... , n)$ such that $1 \leq |a_{k}-k | \leq 2$ for all $k$. Show that $\frac{7}{4}S_{n-1}< S_{n}< 2 S_{n-1}$ for $n > 6.$
There exists a positive integer $b$ such that the base-$10$ fraction $\tfrac{59}{48}$ can be expressed as $1.\overline{14}_b$ (or $1.141414\ldots_b$), a value in base $b$. Find $b$.
$\textbf{(A) }5\qquad\textbf{(B) }6\qquad\textbf{(C) }7\qquad\textbf{(D) }8\qquad\textbf{(E) }9$
Let $f:\mathbb{R}\rightarrow (0,\infty)$ be continuous function of period $1$. Prove that for any $a\in\mathbb{R}$ $$\int_0^1\frac{f(x)}{f(x+a)}dx\geq 1.$$
Let there be $2n+1$ distinct points on a circle. Consider the set of distances between any two out of the $2n+1$ points. What is the smallest size of this set?
[i]Radu Bumbăcea[/i]
Four whole numbers, when added three at a time, give the sums $180$, $197$, $208$, and $222$. What is the largest of the four numbers?
$\text{(A)} \ 77 \qquad \text{(B)} \ 83 \qquad \text{(C)} \ 89 \qquad \text{(D)} \ 95 \qquad \text{(E)} \ \text{cannot be determined}$
Suppose convex hexagon $ \text{HEXAGN}$ has $ 120^\circ$-rotational symmetry about a point $ P$—that is, if you rotate it $ 120^\circ$ about $ P$, it doesn't change. If $ PX\equal{}1$, find the area of triangle $ \triangle{GHX}$.
Deepali has a bag containing 10 red marbles and 10 blue marbles (and nothing else). She removes a random marble from the bag. She keeps doing so until all of the marbles remaining in the bag have the same color. Compute the probability that Deepali ends with exactly 3 marbles remaining in the bag.
Let $n\ge 3$ be a positive integer. Find the largest real number $t_n$ as a function of $n$ such that the inequality
\[\max\left(|a_1+a_2|, |a_2+a_3|, \dots ,|a_{n-1}+a_{n}| , |a_n+a_1|\right) \ge t_n \cdot \max(|a_1|,|a_2|, \dots ,|a_n|)\]
holds for all real numbers $a_1, a_2, \dots , a_n$ .
[i]Proposed by Rohan Goyal and Rijul Saini[/i]
In scalene $\triangle ABC$, $I$ is the incenter, $I_a$ is the $A$-excenter, $D$ is the midpoint of arc $BC$ of the circumcircle of $ABC$ not containing $A$, and $M$ is the midpoint of side $BC$. Extend ray $IM$ past $M$ to point $P$ such that $IM = MP$. Let $Q$ be the intersection of $DP$ and $MI_a$, and $R$ be the point on the line $MI_a$ such that $AR\parallel DP$. Given that $\frac{AI_a}{AI}=9$, the ratio $\frac{QM} {RI_a}$ can be expressed in the form $\frac{m}{n}$ for two relatively prime positive integers $m,n$. Compute $m+n$.
[i]Ray Li.[/i]
[hide="Clarifications"][list=1][*]"Arc $BC$ of the circumcircle" means "the arc with endpoints $B$ and $C$ not containing $A$".[/list][/hide]
Find all real parameters $p$ for which the equation $x^3 -2p(p+1)x^2+(p^4 +4p^3 -1)x-3p^3 = 0$
has three distinct real roots which are sides of a right triangle.
Let $p = 2017$ be a prime number. Let $E$ be the expected value of the expression \[3 \;\square\; 3 \;\square\; 3 \;\square\; \cdots \;\square\; 3 \;\square\; 3\] where there are $p+3$ threes and $p+2$ boxes, and one of the four arithmetic operations $\{+, -, \times, \div\}$ is uniformly chosen at random to replace each of the boxes. If $E = \tfrac{m}{n}$, where $m$ and $n$ are relatively prime positive integers, find the remainder when $m+n$ is divided by $p$.
[i]Proposed by Michael Tang[/i]
Various points $x_1,..., x_n$ ($n \ge 3$) are randomly located on the $Ox$ axis. Construct all parabolas defined by the monic square trinomials and intersecting the Ox axis at these points (and not intersecting axis at other points). Let$ y = f_1$, $...$ , $y = f_m$ are functions that define these parabolas. Prove that the parabola $y = f_1 +...+ f_m$ intersects the $Ox$ axis at two points.
Each corner of a rectangular prism is cut off. Two (of the eight) cuts are shown. How many edges does the new figure have?
[asy]
draw((0,0)--(3,0)--(3,3)--(0,3)--cycle);
draw((3,0)--(5,2)--(5,5)--(2,5)--(0,3));
draw((3,3)--(5,5));
draw((2,0)--(3,1.8)--(4,1)--cycle,linewidth(1));
draw((2,3)--(4,4)--(3,2)--cycle,linewidth(1));[/asy]
$ \text{(A)}\ 24\qquad\text{(B)}\ 30\qquad\text{(C)}\ 36\qquad\text{(D)}\ 42\qquad\text{(E)}\ 48 $
[i]Assume that the planes cutting the prism do not intersect anywhere in or on the prism.[/i]