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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
May 1, 2025
May is an exciting month! National MATHCOUNTS is the second week of May in Washington D.C. and our Founder, Richard Rusczyk will be presenting a seminar, Preparing Strong Math Students for College and Careers, on May 11th.

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[*]May 21st, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 2 Math Jam, Problems 5 and 6, Canada/USA Mathcamp staff will discuss solutions to Problems 5 and 6 of the 2025 Mathcamp Qualifying Quiz![/list]
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0 replies
jlacosta
May 1, 2025
0 replies
9 Prodigy AoPS or Khanacadamy
ZMB038   13
N a few seconds ago by greenplanet2050
Hey everyone just was wondering what everybody prefers? Try not to fight so this doesn't get locked!
13 replies
ZMB038
Today at 1:15 PM
greenplanet2050
a few seconds ago
max number of candies
orangefronted   30
N 11 minutes ago by Creeperboat
A store sells a strawberry flavoured candy for 1 dollar each. The store offers a promo where every 4 candy wrappers can be exchanged for one candy. If there is no limit to how many times you can exchange candy wrappers for candies, what is the maximum number of candies I can obtain with 100 dollars?
30 replies
orangefronted
Apr 3, 2025
Creeperboat
11 minutes ago
9 How many squares do you have memorized
LXC007   88
N 19 minutes ago by A7456321
How many squares have you memorized. I have 1-20

Edit: to clarify i mean positive squares from 1 so if you say ten you mean you memorized the squares 1,2,3,4,5,6,7,8,9 and 10
88 replies
LXC007
May 17, 2025
A7456321
19 minutes ago
Help to make it clear on basic Concept
Miranda2829   2
N 30 minutes ago by UberPiggy
Where I use extraneous solution in equation?
Why square of both side we will have plus and minus answer?
2 replies
Miranda2829
3 hours ago
UberPiggy
30 minutes ago
Inequalities
sqing   16
N Today at 4:01 PM by DAVROS
Let $ a,b,c\geq 0 ,a+b+c\leq 3. $ Prove that
$$a^2+b^2+c^2+ab +2ca+2bc +  abc \leq \frac{251}{27}$$$$ a^2+b^2+c^2+ab+2ca+2bc  + \frac{2}{5}abc  \leq \frac{4861}{540}$$$$ a^2+b^2+c^2+ab+2ca+2bc  + \frac{7}{20}abc  \leq \frac{2381411}{26460}$$
16 replies
sqing
Yesterday at 12:47 PM
DAVROS
Today at 4:01 PM
Inequalities
sqing   0
Today at 2:26 PM
Let $ a,b,c\geq 0 $ and $ab+bc+ca =1.$ Prove that
$$(a^2+b^2+c^2)(a+b+c-2)\ge 8abc(1-a-b-c) $$$$(a^2+b^2+c^2)(a+b+c-\frac{5}{2})\ge 2abc(1-a-b-c) $$
0 replies
sqing
Today at 2:26 PM
0 replies
A suspcious assumption
NamelyOrange   1
N Today at 1:55 PM by NamelyOrange
Let $a,b,c,d$ be positive integers. Maximize $\max(a,b,c,d)$ if $a+b+c+d=a^2-b^2+c^2-d^2=2012$.
1 reply
NamelyOrange
Today at 1:53 PM
NamelyOrange
Today at 1:55 PM
Maximum value of function (with two variables)
Saucepan_man02   1
N Today at 1:39 PM by Saucepan_man02
If $f(\theta) = \min(|2x-7|+|x-4|+|x-2 -\sin \theta|)$, where $x, \theta \in \mathbb R$, then maximum value of $f(\theta)$.
1 reply
Saucepan_man02
Today at 1:25 PM
Saucepan_man02
Today at 1:39 PM
It is given that $M=1+\frac12+\frac13+\frac14+\cdots+\frac{1}{23}=\frac{n}{23!},
Vulch   3
N Today at 11:58 AM by mohabstudent1
It is given that $M=1+\frac12+\frac13+\frac14+\cdots+\frac{1}{23}=\frac{n}{23!},$ where $n$ is a natural number.What is the remainder when $n$ is divided by $13?$
3 replies
Vulch
Apr 9, 2025
mohabstudent1
Today at 11:58 AM
Vieta's Relations
P162008   8
N Today at 11:53 AM by mohabstudent1
If $\alpha,\beta$ and $\gamma$ are the roots of the cubic equation $x^3 - x^2 + 2x - 3 = 0.$
Evaluate $\sum_{cyc} \frac{\alpha^3 - 3}{\alpha^2 - 2}$
Is there any alternate approach except just bash
8 replies
P162008
Yesterday at 10:11 PM
mohabstudent1
Today at 11:53 AM
[PMO22 Areas I.5] Double log equation
aops-g5-gethsemanea2   1
N Today at 10:16 AM by aops-g5-gethsemanea2
Suppose a real number $x>1$ satisfies $$\log_{\sqrt[3]3}(\log_3 x)+\log_3(\log_{27}x)+\log_{27}(\log_{\sqrt[3]3}x)=1.$$Compute $\log_3(\log_3 x)$.

Answer confirmation
1 reply
aops-g5-gethsemanea2
Today at 10:16 AM
aops-g5-gethsemanea2
Today at 10:16 AM
why $sqrt{(x^2 -1)^{2}}$ should be equal to $1-x^2?$
Vulch   5
N Today at 9:38 AM by vanstraelen
In this link, would anyone explain me why $\sqrt{(x^2 -1)^{2}}$ should be equal to $1-x^2?$
5 replies
Vulch
Today at 5:57 AM
vanstraelen
Today at 9:38 AM
Inequalities
sqing   7
N Today at 9:03 AM by sqing
Let $ a,b,c>0. $ Prove that$$a^2+b^2+c^2+abc-k(a+b+c)\geq 3k+2-2(k+1)\sqrt{k+1}$$Where $7\geq k \in N^+.$
$$a^2+b^2+c^2+abc-3(a+b+c)\geq-5$$
7 replies
sqing
May 20, 2025
sqing
Today at 9:03 AM
Inequalities
sqing   2
N Today at 6:42 AM by sqing
Let $ a,b,c> 0 , a^3+b^3+c^3+abc =4.$ Prove that
$$ (a+b)(c+1) \leq 4$$Let $ a,b> 0 ,  a^3+b^3+ab =3.$ Prove that
$$ (a+b) (a+1) (b+1) \leq 8$$
2 replies
sqing
Today at 5:33 AM
sqing
Today at 6:42 AM
math problems
fruitmonster97   9
N Dec 23, 2024 by Amkan2022
If the average of the set $5,x,10,10,10,10$ is $x,$ what is the value of $x$?

Compute the two-digit base $10$ number $n$ such that $n_9+n_7=n_{20}.$

William is ordering bottles. There are eight colors of bottles: White, Red, Blue, Green, Orange, Purple, Yellow, and Charteruse. What is the probability he puts the red bottle first and the white bottle last?

A paper towel roll is a cylinder with another cylinder in the middle cut out. Trying to save money, a CEO of a paper towel company makes the inside radius increase by $10\%.$ He is then sued, and forced to lower the price to match the original ratio of paper towel to cost. By what percentage does he lower the cost?

Eleven elves are making christmas presents. Each makes the same number of presents, and the sum of the digits of the total number of presents is $11.$ Also, after two elves steal all of the presents they made, the remaining number of presents ends in $5.$ How many presents did the two steal?

9 replies
fruitmonster97
Dec 23, 2024
Amkan2022
Dec 23, 2024
math problems
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fruitmonster97
2501 posts
#1
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If the average of the set $5,x,10,10,10,10$ is $x,$ what is the value of $x$?

Compute the two-digit base $10$ number $n$ such that $n_9+n_7=n_{20}.$

William is ordering bottles. There are eight colors of bottles: White, Red, Blue, Green, Orange, Purple, Yellow, and Charteruse. What is the probability he puts the red bottle first and the white bottle last?

A paper towel roll is a cylinder with another cylinder in the middle cut out. Trying to save money, a CEO of a paper towel company makes the inside radius increase by $10\%.$ He is then sued, and forced to lower the price to match the original ratio of paper towel to cost. By what percentage does he lower the cost?

Eleven elves are making christmas presents. Each makes the same number of presents, and the sum of the digits of the total number of presents is $11.$ Also, after two elves steal all of the presents they made, the remaining number of presents ends in $5.$ How many presents did the two steal?
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jocaleby1
204 posts
#2
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3
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NS0004
191 posts
#3
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1. (45+x)/6 = x so 45 +x = 6x so x = 9
3. You have 8! ways to order the bottles so the denominator will be 40320, Out of these you have 1 way to put the red bottle first and 1 way to put the white bottle last and 6! ways to order the middle 6 bottles. So the number of ways to put the red bottle first and the white bottle last is 6!= 720. So the probability will be 720/40320 which is 8!/6! which is just 1/56 because all the other terms cancel out. So the answer for number 3 is 1/56.
5. The restraints on the total number of presents, is that the digits must sum to 11 and the number must be divisible by 11. The only number that satisfies these constraints is 308 which 11 x 28. So each elf made 28 presents which means the presents that two of them stole is 2x28=56
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fruitmonster97
2501 posts
#4
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$308$ is not the only multiple of $11$ with a digit sum of $11.$
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pingpongmerrily
3732 posts
#5
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sol 1
sol 2
More coming later
This post has been edited 1 time. Last edited by pingpongmerrily, Dec 23, 2024, 5:17 PM
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fruitmonster97
2501 posts
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$28_7$ isn't possible, as $8$ is not a digit in bae $7.$
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pingpongmerrily
3732 posts
#7
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fruitmonster97 wrote:
$28_7$ isn't possible, as $8$ is not a digit in bae $7.$

oh that's why there were two solutions which seemed off

ok let me fix that
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NS0004
191 posts
#8
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5. I just realized my mistake on problem 5, didnt read that after the presents of the two stealing elves were subtracted the number ended in 5. The correct answer is 110 because the total presents was 11x55 = 605. When 110 is subtracted from 605, you get 495 which ends in 5.
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NS0004
191 posts
#9
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Also I just realized I made a small mistake in my solution for question 2 as I said, "So the probability will be 720/40320 which is 8!/6!" I meant to say 6!/8! instead.
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Amkan2022
2024 posts
#10
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P4 depends on the ratio of the radii of the two cylinders.
Its not a valid degree of freedom, I believe
This post has been edited 1 time. Last edited by Amkan2022, Dec 23, 2024, 5:29 PM
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