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Expected number of flips
Bread10   8
N 3 hours ago by mathprodigy2011
An unfair coin has a $\frac{4}{7}$ probability of coming up heads and $\frac{3}{7}$ probability of coming up tails. The expected number of flips necessary to first see the sequence $HHTHTHHT$ in that consecutive order can be written as $\frac{m}{n}$ for relatively prime positive integers $m$, $n$. Find the number of factors of $n$.

$\textbf{(A)}~40\qquad\textbf{(B)}~42\qquad\textbf{(C)}~44\qquad\textbf{(D)}~45\qquad\textbf{(E)}~48$
8 replies
Bread10
Yesterday at 8:58 PM
mathprodigy2011
3 hours ago
Help with Competitive Geometry?
REACHAW   3
N 5 hours ago by REACHAW
Hi everyone,
I'm struggling a lot with geometry. I've found algebra, number theory, and even calculus to be relatively intuitive. However, when I took geometry, I found it very challenging. I stumbled my way through the class and can do the basic 'textbook' geometry problems, but still struggle a lot with geometry in competitive math. I find myself consistently skipping the geometry problems during contests (even the easier/first ones).

It's difficult for me to see the solution path. I can do the simpler textbook tasks (eg. find congruent triangles) but not more complex ones (eg. draw these two lines to form similar triangles).

Do you have any advice, resources, or techniques I should try?
3 replies
REACHAW
Monday at 11:51 PM
REACHAW
5 hours ago
fractional part
Ecrin_eren   3
N Yesterday at 9:26 PM by rchokler
{x^2}+{x}=0.64

How many positive real values of x satisfy this equation?
3 replies
Ecrin_eren
Apr 13, 2025
rchokler
Yesterday at 9:26 PM
Angle oriented geometry
Problems_eater   0
Yesterday at 9:03 PM
Let $A, B, C,D$ be four distinct points in the plane.
Which of the following statements, expressed using oriented angles, are always true?

1.If lines $AB$ and $CD$ are distinct and parallel, then
the oriented angle $ABC$ is equal to the oriented angle DCB.

2.If $B$ lies on the segment $AC$, then
the oriented angle $DBA$ plus the oriented angle $DBC $equals $180°$.

3.If the oriented angle$ ABC$ plus the oriented angle $BCD$ equals 0°, then
lines $AB $and $CD$ are parallel.

4.If the oriented angle $ABC$ plus the oriented angle $BCD$ equals $180°$, then
lines $AB$ and $CD$are parallel.
0 replies
Problems_eater
Yesterday at 9:03 PM
0 replies
how many quadrilaterals ?
Ecrin_eren   6
N Yesterday at 5:31 PM by mathprodigy2011
"All the diagonals of an 11-gon are drawn. How many quadrilaterals can be formed using these diagonals as sides? (The vertices of the quadrilaterals are selected from the vertices of the 11-gon.)"
6 replies
Ecrin_eren
Apr 13, 2025
mathprodigy2011
Yesterday at 5:31 PM
Plane geometry problem with inequalities
ReticulatedPython   3
N Yesterday at 2:48 PM by vanstraelen
Let $A$ and $B$ be points on a plane such that $AB=1.$ Let $P$ be a point on that plane such that $$\frac{AP^2+BP^2}{(AP)(BP)}=3.$$Prove that $$AP \in \left[\frac{5-\sqrt{5}}{10}, \frac{-1+\sqrt{5}}{2}\right] \cup \left[\frac{5+\sqrt{5}}{10}, \frac{1+\sqrt{5}}{2}\right].$$
Source: Own
3 replies
ReticulatedPython
Apr 10, 2025
vanstraelen
Yesterday at 2:48 PM
Inequalities
sqing   1
N Yesterday at 1:55 PM by sqing
Let $   a,b    $ be reals such that $  a^2-ab+b^2 =3$ . Prove that
$$  \frac{13}{ 10 }> \frac{1}{ a^2+1 }+ \frac{1}{ b^2+1 } \geq \frac{1}{ 2 }$$$$   \frac{6}{ 5 }>\frac{1}{ a^4+1 }+ \frac{1}{ b^4+1 } \geq   \frac{1}{ 5 }$$$$  \frac{1}{ a^6+1 }+ \frac{1}{ b^6+1 } \geq   \frac{1}{ 14 }$$
1 reply
sqing
Yesterday at 8:59 AM
sqing
Yesterday at 1:55 PM
idk12345678 Math Contest
idk12345678   21
N Yesterday at 1:25 PM by idk12345678
Welcome to the 1st idk12345678 Math Contest.
You have 4 hours. You do not have to prove your answers.
Post \signup username to sign up. Post your answers in a hide tag and I will tell you your score.*


The contest is attached to the post

Clarifications

*I mightve done them wrong feel free to ask about an answer
21 replies
idk12345678
Apr 10, 2025
idk12345678
Yesterday at 1:25 PM
purple comet math competition question
AVY2024   4
N Yesterday at 1:02 PM by K1mchi_
Given that (1 + tan 1)(1 + tan 2). . .(1 + tan 45) = 2n, find n
4 replies
AVY2024
Yesterday at 11:00 AM
K1mchi_
Yesterday at 1:02 PM
Inequalities
sqing   25
N Yesterday at 12:06 PM by sqing
Let $ a,b,c,d>0 $ and $(a+c)(b+d)=ac+\frac{3}{2}bd.$ Prove that
$$\frac{a}{b}+\frac{b}{c}+\frac{c}{d}+\frac{d}{a}\geq \frac{20-\sqrt{10}}{3}$$Let $ a,b,c,d>0 $ and $(a+c)(b+d)=ac+\frac{4}{3}bd.$ Prove that
$$\frac{a}{b}+\frac{b}{c}+\frac{c}{d}+\frac{d}{a}\geq \frac{21-\sqrt{6}}{3}$$
25 replies
sqing
Dec 3, 2024
sqing
Yesterday at 12:06 PM
a