Found problems: 85335
A two-digit integer is divided by the sum of its digits. Find the largest remainder that can occur.
Let there be $n$ students and $m$ clubs. The students joined the clubs so that the following is true:
- For all students $x$, you can choose some clubs such that $x$ is the only student who joined all of the chosen clubs.
Let the number of clubs each student joined be $a_1,a_2,...,a_m$. Prove that
$$a_1!(m - a_1)! + a_2!(m - a_2)! + ... + a_n!(m -a_n)! \le m!$$
The function $g$ is defined about the natural numbers and satisfies the following conditions:
$g(2) = 1$
$g(2n) = g(n)$
$g(2n+1) = g(2n) +1.$
Where $n$ is a natural number such that $1 \leq n \leq 2002$.
Find the maximum value $M$ of $g(n).$ Also, calculate how many values of $n$ satisfy the condition of $g(n) = M.$
Consider a function \( n \mapsto f(n) \) that satisfies the following conditions:
\( f(n) \) is an integer for each \( n \).
\( f(0) = 1 \).
\( f(n+1) > f(n) + f(n-1) + \cdots + f(0) \) for each \( n = 0, 1, 2, \dots \).
Determine the smallest possible value of \( f(2023) \).
Solve the equation in the set of real numbers:
$$\left[ x+\frac{1}{x} \right] = \left[ x^2+\frac{1}{x^2} \right]$$
where $[a]$, represents the integer part of the real number $a$.
Ten students take a test consisting of $4$ different papers in Algebra, Geometry, Number Theory and Combinatorics. First, the proctor distributes randomly the Algebra paper to each student. Then the remaining papers are distributed one at a time in the following order: Geometry, Number Theory, Combinatorics in such a way that no student receives a paper before he fi nishes the previous one. In how many ways can the proctor distribute the test papers given that a student may for example nish the Number Theory paper before another student receives the Geometry paper, and that he receives the Combinatorics paper after that the same other student receives the Combinatorics papers.
The vertices of the square $ABCD$ are the centers of four circles, all of which pass through the center of the square. Prove that the intersections of the circles on the square $ABCD$ sides are vertices of a regular octagon.
In a team of guards, each is assigned a different positive integer. For any two guards, the ratio of the two numbers assigned to them is at least $3:1$. A guard assigned the number $n$ is on duty for $n$ days in a row, off duty for $n$ days in a row, back on duty for $n$ days in a row, and so on. The guards need not start their duties on the same day. Is it possible that on any day, at least one in such a team of guards is on duty?
Find all four-digit natural numbers formed by two even digits and two odd digits that verify that when multiplied by $2$ four-digit numbers are obtained with all their even digits and when divided by $2$ four-digit natural numbers are obtained with all their odd digits.
Bo, Coe, Flo, Joe, and Moe have different amounts of money. Neither Jo nor Bo has as much money as Flo. Both Bo and Coe have more than Moe. Jo has more than Moe, but less than Bo. Who has the least amount of money?
$ \text{(A)}\ \text{Bo}\qquad\text{(B)}\ \text{Coe}\qquad\text{(C)}\ \text{Flo}\qquad\text{(D)}\ \text{Joe}\qquad\text{(E)}\ \text{Moe} $
Consider a $ n \times n$ checkerboard with $ n > 1, n \in \mathbb{N}.$ How many possibilities are there to put $ 2n \minus{} 2$ identical pebbles on the checkerboard (each on a different field/place) such that no two pebbles are on the same checkerboard diagonal. Two pebbles are on the same checkerboard diagonal if the connection segment of the midpoints of the respective fields are parallel to one of the diagonals of the $ n \times n$ square.
For any positive integer $n$, define $\boxed{n}$ to be the sum of the positive factors of $n$. For example, $\boxed{6} = 1 + 2 + 3 + 6 = 12$.
Find $\boxed{\boxed{11}}$.
$\textbf{(A)}\ 13 \qquad
\textbf{(B)}\ 20 \qquad
\textbf{(C)}\ 24 \qquad
\textbf{(D)}\ 28 \qquad
\textbf{(E)}\ 30$
In the diagram shown, how many pathways are there from point $A$ to point $B$ if you are only allowed to travel due East, Southeast, or Southwest?
[img]https://cdn.artofproblemsolving.com/attachments/9/1/0a1219fb430c402fef4b7555ddff7c88fec47e.jpg[/img]
There is some natural number $n>1$ on the board. Operation is adding to number on the board it maximal non-trivial divisor. Prove, that after some some operations we get number, that is divisible by $3^{2000}$
[i]A. Golovanov[/i]
8 chess players participated in the chess tournament and everyone played exactly one game with everyone else. It is known that any two chess players who play a draw with each other ended up scoring different numbers of points. Find the greatest possible number of draws in this tournament. (For winning the game the chess player is awarded $1$ point, for a draw $1/2$ points, for defeat $0$ points.)
Find all positive integers $n$ such that $-5^4 + 5^5 + 5^n$ is a perfect square. Do the same for $2^4 + 2^7 + 2^n.$
Each vertex of a convex polygon has integer coordinates, and no side of this polygon is horizontal or vertical. Prove that the sum of the lengths of the segments of lines of the form $x = m$, $m$ an integer, that lie within the polygon is equal to the sum of the lengths of the segments of lines of the form $y = n$, $n$ an integer, that lie within the polygon.
(G Galperin)
Thirty pupils from the same class decided to exchange visits. Any pupil may make several visits during one evening, but must stay home if he is receiving guests that evening. Prove that in order that each pupil visit each of his classmates
(a) four evenings are not enough
(b) five evenings are not enough
(c) ten evenings are enough
(d) even seven evenings are enough
$\Delta ABC$ is a triangle with center $I$ of its inscribed circle and $B_1$ and $C_1$ are feet of its angle bisectors through $B$ and $C$. Let $S$ be the middle point on the arc $\widehat{BAC}$ of the circumscribed circle of $\Delta ABC$ (denoted with $\Omega$) and let $\omega_a$ be the excircle of $\Delta ABC$ opposite to $A$. Let $\omega_a (I_a)$ be tangent to $AB$ and $AC$ in points $D$ and $E$ respectively and $SI\cap \Omega=\{S,P\}$. Let $M$ be the middle point of $DE$ and $N$ be the middle point of $SI$. If $MN\cap AP=K$, prove that $KI_a\perp B_1 C_1$.
In acute triangle $ABC$, $D,E$ are two points on side $BC$, satisfying that $\angle BAE=\angle CAF$. $FM\perp AB,EN\perp AC$ ($M,N$ are foot points). $AE$ intersects the circumcircle of $\triangle ABC$ at $D$. Prove that the area of $\triangle ABC$ and quadrilateral $AMDN$ are equal.
We are given a finite number of functions of the form $y = c2^{-|x-d|}$. In each case $c$ and $d$ are parameters with $c > 0$. The function $f(x)$ is defined on the interval $[a, b]$ as follows: For each $x$ in $[a, b]$, $f(x)$ is the maximum value taken by any of the given functions $y$ (defined above) at that point $x$. It is known that $f(a) = f(b)$. Prove that the total length of the intervals in which the function $f$ is increasing is equal to the total length of the intervals in which it is decreasing (that is, both are equal to $(b- a)/2$ ).
(NB Vasiliev)
Let $a,b,b',c,m,q$ be positive integers, where $m>1,q>1,|b-b'|\ge a$. It is given that there exist a positive integer $M$ such that
$$S_q(an+b)\equiv S_q(an+b')+c\pmod{m}$$
holds for all integers $n\ge M$. Prove that the above equation is true for all positive integers $n$. (Here $S_q(x)$ is the sum of digits of $x$ taken in base $q$).
Determine the maximal possible length of the sequence of consecutive integers which are expressible in the form $ x^3\plus{}2y^2$, with $ x, y$ being integers.
On each of the $2014^2$ squares of a $2014 \times 2014$-board a light bulb is put. Light bulbs can be either on or off. In the starting situation a number of the light bulbs is on. A move consists of choosing a row or column in which at least $1007$ light bulbs are on and changing the state of all $2014$ light bulbs in this row or column (from on to off or from off to on). Find the smallest non-negative integer $k$ such that from each starting situation there is a finite sequence of moves to a situation in which at most $k$ light bulbs are on.
For a natural number $b$, let $N(b)$ denote the number of natural numbers $a$ for which the equation $x^2 + ax + b = 0$ has integer roots. What is the smallest value of $b$ for which $N(b) = 20$?