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k a April Highlights and 2025 AoPS Online Class Information
jlacosta   0
Yesterday at 3:18 PM
Spring is in full swing and summer is right around the corner, what are your plans? At AoPS Online our schedule has new classes starting now through July, so be sure to keep your skills sharp and be prepared for the Fall school year! Check out the schedule of upcoming classes below.

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[*]April 22nd (Webinar), 4:00pm PT/7:00pm ET, Competitive Programming at AoPS (USACO).[/list]
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0 replies
jlacosta
Yesterday at 3:18 PM
0 replies
Easy Problem
MathleteMystic   1
N an hour ago by Sadigly
Prove that among n integers we can always choose some of them whose sum is a multiple on n.

I do have a solution to this, but could someone write a more descriptive one, please? Something like the logic behind it...
1 reply
MathleteMystic
an hour ago
Sadigly
an hour ago
Number of solutions
Ecrin_eren   0
3 hours ago
The given equation is:

x³ + 4y³ + 2y = (2024 + 2y)(xy + 1)

The question asks for the number of integer solutions.

0 replies
Ecrin_eren
3 hours ago
0 replies
Probability
Ecrin_eren   0
3 hours ago
In a board, James randomly writes A , B or C in each cell. What is the probability that, for every row and every column, the number of A 's modulo 3 is equal to the number of B's modulo 3?

0 replies
Ecrin_eren
3 hours ago
0 replies
Congruence
Ecrin_eren   0
4 hours ago
Find the number of integer pairs (x, y) satisfying the congruence equation:

3y² + 3x²y + y³ ≡ 3x² (mod 41)

for 0 ≤ x, y < 41.

0 replies
Ecrin_eren
4 hours ago
0 replies
No more topics!
2025 USC Math Comp (SCMC) individual round
Bluesoul   0
Mar 30, 2025
1. For an integer $x,$ we define a \textit{step} as either doubling the value of the integer or subtracting 3 from it. What is the minimum number of steps required to obtain 25 from 11?
2. Find the sum of all integer values of $n$ that satisfy the inequality chain \[n^3<2025<3^n.\]3. A rectangle with length 20 units and height 16 units is divided into 10 smaller congruent rectangles. Let $P$ be the largest possible perimeter of one of these small rectangles; compute the value of $10P.$
4. Positive integers $x,y,z$ satisfy the system
\[\left\{\begin{array}{l}
	x^2+y^2=z^2+22\\
	y^2+z^2=x^2+76\\
	x^2+z^2=y^2-4.
	\end{array}
	\right.\]What is the value of $xyz?$
5. \begin{problem}
Four husband-wife couples go ballroom dancing one evening. The husbands' names are Henry, Peter, Steve, and Roger, while the wives' names are Elizabeth, Keira, Mary, and Anne. At a given moment, Henry's wife is dancing with Elizabeth's husband, who is not Henry; Roger and Anne are not dancing; Peter is playing the trumpet; and Mary is playing the piano. Given that Anne's husband is not Peter, how many different letters are in the name of Roger's wife?
6. A laser is fired from vertex $A$ into the interior of regular hexagon $ABCDEF,$ whose sides are mirrors, and hits side $\overline{CD}$ at $G.$ It then reflects and hits $\overline{AF}$ at $H,$ and finally reflects and hits $\overline{DE}$ at $I.$ If $\angle BAG=45^\circ,$ then how many degrees are in $\angle HIE?$
7. What is the value of the expression
\[\frac{\log_2(\log_2 3)}{\log_4(\log_4 9)}?\]8. The area of equiangular octagon $ABCDEFGH,$ with $AB=EF=2,$ $BC=FG=3,$ $CD=GH=4,$ and $DE=AH=5,$ can be written in the form $a+b\sqrt{2}$, find $a+b$.
9. A toe-wrestling tournament between Don and Kam consists of three matches. In each match, the winner is the first person to reach five points. After the three matches, each person’s score is the number of matches they won, plus the sum of the points they earned during all of their matches. Let $d$ and $k$ denote Don and Kam’s final scores, respectively. How many ordered pairs $(d, k)$ are possible?
10. For each positive integer $n$, let $s(n)$ denote the sum of the remainders when $n$ is divided by $2,3,4,5,$ and $6.$ For example, when $n=93,$ we have $s(93)=1+0+1+3+3=8.$ Compute the integer $N$ for which \[\sum_{n=1}^{N}s(n)=2025.\]11. For complex numbers $z,$ we define the function \[f(z)=\frac{z+3}{z-2i}.\]Over all values of $z$ for which $f(z)$ is real, the minimum possible value of $|z|^2$ can be written in the form $\dfrac{m}{n}$ for positive integers $m$ and $n.$ Compute the value of $100m+n.$
12. In convex quadrilateral $ABCD,$ $AB=6, BC=10,$ and $\angle{ABC}=90^{\circ}$. Let $M$ and $N$ be the midpoints of $\overline{AD}$ and $\overline{CD},$ respectively. Compute the area of $\triangle{BMN},$ given that the area of $ABCD$ is $50$.
13. What is the remainder when $20^{25}$ is divided by 2025?
14. Your friend plays a prank on you by changing your phone's password. Your friend chooses a password consisting of 4 decimal digits $\overline{abcd}$ uniformly at random and tells you the sum of its digits. (Leading zeros are allowed, so your friend can choose any password from 0000, 0001, and so on to 9999.) Then, you select a digit $e;$ your friend tells you the password if and only if $e$ is the median of the set $\{a,b,c,d,e\}.$
\null
Now, your friend picks a password whose digits sum to 20; let $S$ be the set of all such passwords. Suppose you select $e$ such that the probability that your friend tells you the password, given this information, is maximized. Compute the number of passwords in $S$ for which this would not occur, given your choice of $e.$
15. For real numbers $x,$ we define the function \[f(x)=\lceil{1+\sqrt{x+1}}\rceil+\lfloor{1-\sqrt{x-1}}\rfloor.\]Compute the $100^\text{th}-$smallest integer $x$ for which $f(x)=2$.
16. How many ordered pairs $(x,y),$ with $1\le x,y\le 100,$ satisfy the congruence \[2^{2^x+2^y}\equiv 1\pmod{101}?\]17. $\triangle ABC$ has circumcircle $\omega$ and incenter $I.$ $\overline{AI}$ is extended to intersect $\omega$ at a point $P\ne A,$ and $\overline{BI}$ is extended to intersect $\overline{AC}$ at $Q.$ If $AB=5,$ $BC=8,$ and $IPCQ$ is a cyclic quadrilateral, then compute $AC^2.$
18. The $\textbf{Cantor set}$ is constructed as follows:
i) Start with the closed interval $[0, 1]$.
ii)Remove the open middle third of the interval, so we remove $\left(\frac{1}{3}, \frac{2}{3}\right)$ at first and leave $\left[0, \frac{1}{3}\right]$ and $\left[\frac{2}{3}, 1\right]$.
iii) Remove the open middle third from each of the remaining closed intervals, and repeat this step infinitely.
For how many integer values of $i$, where $0 \leq i \leq 10$, is $\frac{i}{10}$ an element of the Cantor set?
19. For complex numbers $a,b,c$ satisfying $|a|^2+|b|^2+|c|^2=1$, the maximum value of $|ab(a^2-b^2)+ca(c^2-a^2)+bc(b^2-c^2)|$ can be expressed in the simplest form of $\frac{p}{q}, \gcd(p,q)=1$, find $p+q$.
20. Consider cyclic quadrilateral $ABCD$ with all integer side lengths and $AB=AD=6$. Let $AC$ meet $BD$ at $F$, $AF=3,CF=9$. Denote the centers of the circumcircles of polygons $CBF, ABCD, DCF$ as $H,I,J$ respectively. Compute the area of $\triangle{HIJ}$. The answer is in the simplest form of $\frac{p\sqrt{q}}{r},\gcd(p,r)=1$ and $q$ is square-free, compute $p+q+r$.
0 replies
Bluesoul
Mar 30, 2025
0 replies
2025 USC Math Comp (SCMC) individual round
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Bluesoul
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1. For an integer $x,$ we define a \textit{step} as either doubling the value of the integer or subtracting 3 from it. What is the minimum number of steps required to obtain 25 from 11?
2. Find the sum of all integer values of $n$ that satisfy the inequality chain \[n^3<2025<3^n.\]3. A rectangle with length 20 units and height 16 units is divided into 10 smaller congruent rectangles. Let $P$ be the largest possible perimeter of one of these small rectangles; compute the value of $10P.$
4. Positive integers $x,y,z$ satisfy the system
\[\left\{\begin{array}{l}
	x^2+y^2=z^2+22\\
	y^2+z^2=x^2+76\\
	x^2+z^2=y^2-4.
	\end{array}
	\right.\]What is the value of $xyz?$
5. \begin{problem}
Four husband-wife couples go ballroom dancing one evening. The husbands' names are Henry, Peter, Steve, and Roger, while the wives' names are Elizabeth, Keira, Mary, and Anne. At a given moment, Henry's wife is dancing with Elizabeth's husband, who is not Henry; Roger and Anne are not dancing; Peter is playing the trumpet; and Mary is playing the piano. Given that Anne's husband is not Peter, how many different letters are in the name of Roger's wife?
6. A laser is fired from vertex $A$ into the interior of regular hexagon $ABCDEF,$ whose sides are mirrors, and hits side $\overline{CD}$ at $G.$ It then reflects and hits $\overline{AF}$ at $H,$ and finally reflects and hits $\overline{DE}$ at $I.$ If $\angle BAG=45^\circ,$ then how many degrees are in $\angle HIE?$
7. What is the value of the expression
\[\frac{\log_2(\log_2 3)}{\log_4(\log_4 9)}?\]8. The area of equiangular octagon $ABCDEFGH,$ with $AB=EF=2,$ $BC=FG=3,$ $CD=GH=4,$ and $DE=AH=5,$ can be written in the form $a+b\sqrt{2}$, find $a+b$.
9. A toe-wrestling tournament between Don and Kam consists of three matches. In each match, the winner is the first person to reach five points. After the three matches, each person’s score is the number of matches they won, plus the sum of the points they earned during all of their matches. Let $d$ and $k$ denote Don and Kam’s final scores, respectively. How many ordered pairs $(d, k)$ are possible?
10. For each positive integer $n$, let $s(n)$ denote the sum of the remainders when $n$ is divided by $2,3,4,5,$ and $6.$ For example, when $n=93,$ we have $s(93)=1+0+1+3+3=8.$ Compute the integer $N$ for which \[\sum_{n=1}^{N}s(n)=2025.\]11. For complex numbers $z,$ we define the function \[f(z)=\frac{z+3}{z-2i}.\]Over all values of $z$ for which $f(z)$ is real, the minimum possible value of $|z|^2$ can be written in the form $\dfrac{m}{n}$ for positive integers $m$ and $n.$ Compute the value of $100m+n.$
12. In convex quadrilateral $ABCD,$ $AB=6, BC=10,$ and $\angle{ABC}=90^{\circ}$. Let $M$ and $N$ be the midpoints of $\overline{AD}$ and $\overline{CD},$ respectively. Compute the area of $\triangle{BMN},$ given that the area of $ABCD$ is $50$.
13. What is the remainder when $20^{25}$ is divided by 2025?
14. Your friend plays a prank on you by changing your phone's password. Your friend chooses a password consisting of 4 decimal digits $\overline{abcd}$ uniformly at random and tells you the sum of its digits. (Leading zeros are allowed, so your friend can choose any password from 0000, 0001, and so on to 9999.) Then, you select a digit $e;$ your friend tells you the password if and only if $e$ is the median of the set $\{a,b,c,d,e\}.$
\null
Now, your friend picks a password whose digits sum to 20; let $S$ be the set of all such passwords. Suppose you select $e$ such that the probability that your friend tells you the password, given this information, is maximized. Compute the number of passwords in $S$ for which this would not occur, given your choice of $e.$
15. For real numbers $x,$ we define the function \[f(x)=\lceil{1+\sqrt{x+1}}\rceil+\lfloor{1-\sqrt{x-1}}\rfloor.\]Compute the $100^\text{th}-$smallest integer $x$ for which $f(x)=2$.
16. How many ordered pairs $(x,y),$ with $1\le x,y\le 100,$ satisfy the congruence \[2^{2^x+2^y}\equiv 1\pmod{101}?\]17. $\triangle ABC$ has circumcircle $\omega$ and incenter $I.$ $\overline{AI}$ is extended to intersect $\omega$ at a point $P\ne A,$ and $\overline{BI}$ is extended to intersect $\overline{AC}$ at $Q.$ If $AB=5,$ $BC=8,$ and $IPCQ$ is a cyclic quadrilateral, then compute $AC^2.$
18. The $\textbf{Cantor set}$ is constructed as follows:
i) Start with the closed interval $[0, 1]$.
ii)Remove the open middle third of the interval, so we remove $\left(\frac{1}{3}, \frac{2}{3}\right)$ at first and leave $\left[0, \frac{1}{3}\right]$ and $\left[\frac{2}{3}, 1\right]$.
iii) Remove the open middle third from each of the remaining closed intervals, and repeat this step infinitely.
For how many integer values of $i$, where $0 \leq i \leq 10$, is $\frac{i}{10}$ an element of the Cantor set?
19. For complex numbers $a,b,c$ satisfying $|a|^2+|b|^2+|c|^2=1$, the maximum value of $|ab(a^2-b^2)+ca(c^2-a^2)+bc(b^2-c^2)|$ can be expressed in the simplest form of $\frac{p}{q}, \gcd(p,q)=1$, find $p+q$.
20. Consider cyclic quadrilateral $ABCD$ with all integer side lengths and $AB=AD=6$. Let $AC$ meet $BD$ at $F$, $AF=3,CF=9$. Denote the centers of the circumcircles of polygons $CBF, ABCD, DCF$ as $H,I,J$ respectively. Compute the area of $\triangle{HIJ}$. The answer is in the simplest form of $\frac{p\sqrt{q}}{r},\gcd(p,r)=1$ and $q$ is square-free, compute $p+q+r$.
This post has been edited 1 time. Last edited by Bluesoul, Mar 30, 2025, 10:31 AM
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