Olympiad problems

2020 AMC 10, 8

What is the value of \[1+2+3-4+5+6+7-8+\cdots+197+198+199-200?\] $\textbf{(A) } 9,800 \qquad \textbf{(B) } 9,900 \qquad \textbf{(C) } 10,000 \qquad \textbf{(D) } 10,100 \qquad \textbf{(E) } 10,200$

2024 AMC 10, 6

Tags: AMC , AMC 10 , 2024 AMC 10b , 2024 AMC , geometry , perimeter

A rectangle has integer side lengths and an area of $2024$. What is the least possible perimeter of the rectangle? $ \textbf{(A) }160 \qquad \textbf{(B) }180 \qquad \textbf{(C) }222 \qquad \textbf{(D) }228 \qquad \textbf{(E) }390 \qquad $

2005 AMC 10, 11

Tags: modular arithmetic , algebra , AMC 10 , recursion , Sequences

The first term of a sequence is 2005. Each succeeding term is the sum of the cubes of the digits of the previous terms. What is the 2005th term of the sequence? $ \textbf{(A)}\ 29\qquad \textbf{(B)}\ 55\qquad \textbf{(C)}\ 85\qquad \textbf{(D)}\ 133\qquad \textbf{(E)}\ 250$

2024 AMC 10, 23

Tags: 2024 AMC 10A , 2024 AMC , AMC , AMC 10 , system of equations , 2024 AMC 12A , AMC 12

Integers $a$, $b$, and $c$ satisfy $ab + c = 100$, $bc + a = 87$, and $ca + b = 60$. What is $ab + bc + ca$? $ \textbf{(A) }212 \qquad \textbf{(B) }247 \qquad \textbf{(C) }258 \qquad \textbf{(D) }276 \qquad \textbf{(E) }284 \qquad $

2021 AMC 10 Spring, 2

Tags: AMC , AMC 10 , AMC 10 A , 2021 AMC 10A

Portia’s high school has $3$ times as many students as Lara’s high school. The two high schools have a total of $2600$ students. How many students does Portia’s high school have? $\textbf{(A) }600 \qquad \textbf{(B) }650 \qquad \textbf{(C) }1950 \qquad \textbf{(D) }2000 \qquad \textbf{(E) }2050$

2013 AMC 10, 5

Tags: AMC , algebra , AMC 10

Tom, Dorothy, and Sammy went on a vacation and agreed to split the costs evenly. During their trip Tom paid $\$105$, Dorothy paid $\$125$, and Sammy paid $\$175$. In order to share the costs equally, Tom gave Sammy $t$ dollars, and Dorothy gave Sammy $d$ dollars. What is $t-d$? $ \textbf{(A)}\ 15\qquad\textbf{(B)}\ 20\qquad\textbf{(C)}\ 25\qquad\textbf{(D)}\ 30\qquad\textbf{(E)}\ 35 $

2023 AMC 10, 8

Tags: AMC , AMC 10 , AMC 10 B , Exponents

What is the units digit of $2022^{2023} + 2023^{2022}$? $\textbf{(A)}~7\qquad\textbf{(B)}~1\qquad\textbf{(C)}~3\qquad\textbf{(D)}~5\qquad\textbf{(E)}~9$

2022 AMC 12/AHSME, 7

Tags: AMC , AMC 10 , statistics , 2022 AMC , 2022 AMC 10B , 2022 AMC 12B , AMC 12

Camila writes down five positive integers. The unique mode of these integers is $2$ greater than their median, and the median is $2$ greater than their arithmetic mean. What is the least possible value for the mode? $\textbf{(A) }5\qquad\textbf{(B) }7\qquad\textbf{(C) }9\qquad\textbf{(D) }11\qquad\textbf{(E) }13$

2021 AMC 10 Spring, 12

Tags: FTW , AMC , AMC 10 , AMC 10 B , Alcumus

Let $N=34 \cdot 34 \cdot 63 \cdot 270$. What is the ratio of the sum of the odd divisors of $N$ to the sum of the even divisors of $N$? $\textbf{(A) }1:16 \qquad \textbf{(B) }1:15 \qquad \textbf{(C) }1:14 \qquad \textbf{(D) }1:8 \qquad \textbf{(E) }1:3$

2021 AMC 10 Fall, 1

Tags: AMC , AMC 10 , AMC 12 , AMC 10 B , AMC 12 B

What is the value of $1234+2341+3412+4123$? $\textbf{(A) } 10,000 \qquad \textbf{(B) }10,010 \qquad \textbf{(C) }10,110 \qquad \textbf{(D) }11,000 \qquad \textbf{(E) }11,110$

2018 AMC 10, 22

Tags: AMC 10 , 2018 AMC 10B , 2018 AMC

Real numbers $x$ and $y$ are chosen independently and uniformly at random from the interval $[0,1]$. Which of the following numbers is closest to the probability that $x,y,$ and $1$ are the side lengths of an obtuse triangle? $\textbf{(A)} \text{ 0.21} \qquad \textbf{(B)} \text{ 0.25} \qquad \textbf{(C)} \text{ 0.29} \qquad \textbf{(D)} \text{ 0.50} \qquad \textbf{(E)} \text{ 0.79}$

2022 AMC 12/AHSME, 22

Tags: AMC , AMC 10 , AMC 12 , 2022 AMC , 2022 AMC 10B , 2022 AMC 12B

Ant Amelia starts on the number line at $0$ and crawls in the following manner. For $n=1,2,3,$ Amelia chooses a time duration $t_n$ and an increment $x_n$ independently and uniformly at random from the interval $(0,1).$ During the $n$th step of the process, Amelia moves $x_n$ units in the positive direction, using up $t_n$ minutes. If the total elapsed time has exceeded $1$ minute during the $n$th step, she stops at the end of that step; otherwise, she continues with the next step, taking at most $3$ steps in all. What is the probability that Amelia’s position when she stops will be greater than $1$? $\textbf{(A) }\frac{1}{3} \qquad \textbf{(B) }\frac{1}{2} \qquad \textbf{(C) }\frac{2}{3} \qquad \textbf{(D) }\frac{3}{4} \qquad \textbf{(E) }\frac{5}{6}$

2017 AMC 10, 2

Tags: AMC , AMC 10 , AMC 10 A , 2017 AMC 10A

Pablo buys popsicles for his friends. The store sells single popsicles for $\$1$ each, 3-popsicle boxes for $\$2$, and 5-popsicle boxes for $\$3$. What is the greatest number of popsicles that Pablo can buy with $\$8$? $\textbf{(A)}\ 8\qquad\textbf{(B)}\ 11\qquad\textbf{(C)}\ 12\qquad\textbf{(D)}\ 13\qquad\textbf{(E)}\ 15$

2020 AMC 12/AHSME, 4

Tags: AMC , AMC 10 , prime numbers , 2020 AMC , 2020 AMC 10B , 2020 AMC 12B , AMC 12

The acute angles of a right triangle are $a^{\circ}$ and $b^{\circ}$, where $a>b$ and both $a$ and $b$ are prime numbers. What is the least possible value of $b$? $\textbf{(A) }2\qquad\textbf{(B) }3\qquad\textbf{(C) }5\qquad\textbf{(D) }7\qquad\textbf{(E) }11$

2012 AMC 10, 19

Tags: geometry , rectangle , AMC , AMC 10 , AMC 10 B , analytic geometry , similar triangles

In rectangle $ABCD$, $AB=6$, $AD=30$, and $G$ is the midpoint of $\overline{AD}$. Segment $AB$ is extended $2$ units beyond $B$ to point $E$, and $F$ is the intersection of $\overline{ED}$ and $\overline{BC}$. What is the area of $BFDG$? $ \textbf{(A)}\ \frac{133}{2}\qquad\textbf{(B)}\ 67\qquad\textbf{(C)}\ \frac{135}{2}\qquad\textbf{(D)}\ 68\qquad\textbf{(E)}\ \frac{137}{2}$

2021 AMC 10 Fall, 4

Tags: AMC 10 B , AMC , AMC 10 , AMC 12 , AMC 12 B

At noon on a certain day, Minneapolis is $N$ degrees warmer than St. Louis. At $4{:}00$ the temperature in Minneapolis has fallen by $5$ degrees while the temperature in St. Louis has risen by $3$ degrees, at which time the temperatures in the two cities differ by $2$ degrees. What is the product of all possible values of $N?$ $(\textbf{A})\: 10\qquad(\textbf{B}) \: 30\qquad(\textbf{C}) \: 60\qquad(\textbf{D}) \: 100\qquad(\textbf{E}) \: 120$

2019 AMC 10, 3

Tags: 2019 AMC 10B , AMC , AMC 10 , percent , 2019 AMC

In a high school with $500$ students, $40\%$ of the seniors play a musical instrument, while $30\%$ of the non-seniors do not play a musical instrument. In all, $46.8\%$ of the students do not play a musical instrument. How many non-seniors play a musical instrument? $\textbf{(A) } 66 \qquad\textbf{(B) } 154 \qquad\textbf{(C) } 186 \qquad\textbf{(D) } 220 \qquad\textbf{(E) } 266$

2013 AMC 10, 13

Tags: complementary counting , AMC , AMC 10

How many three-digit numbers are not divisible by $5$, have digits that sum to less than $20$, and have the first digit equal to the third digit? $\textbf{(A) }52\qquad \textbf{(B) }60\qquad \textbf{(C) }66\qquad \textbf{(D) }68\qquad \textbf{(E) }70\qquad$

2022 AMC 10, 5

Tags: AMC , AMC 10 , 2022 AMC , 2022 AMC 10B , Fractions

What is the value of $\frac{(1+\frac{1}{3})(1+\frac{1}{5})(1+\frac{1}{7})}{\sqrt{(1-\frac{1}{3^2})(1-\frac{1}{5^2})(1-\frac{1}{7^2})}}?$ $\textbf{(A) }\sqrt{3} \qquad \textbf{(B) }2 \qquad \textbf{(C) }\sqrt{15} \qquad \textbf{(D) }4 \qquad \textbf{(E) }\sqrt{105}$

2020 AMC 12/AHSME, 15

Tags: AMC , AMC 12 , 2020 AMC 10B , 2020 AMC , 2020 AMC 12B , counting , AMC 10

There are 10 people standing equally spaced around a circle. Each person knows exactly 3 of the other 9 people: the 2 people standing next to her or him, as well as the person directly across the circle. How many ways are there for the 10 people to split up into 5 pairs so that the members of each pair know each other? $\textbf{(A) } 11 \qquad \textbf{(B) } 12 \qquad \textbf{(C) } 13 \qquad \textbf{(D) } 14 \qquad \textbf{(E) } 15$

2017 AMC 12/AHSME, 14

Tags: AMC , AMC 12 , AMC 12 A , 2017 AMC 12A , AMC 10 , AMC 10 A , combinatorics

Alice refuses to sit next to either Bob or Carla. Derek refuses to sit next to Eric. How many ways are there for the five of them to sit in a row of $5$ chairs under these conditions? $\textbf{(A)}\ 12\qquad\textbf{(B)}\ 16\qquad\textbf{(C)}\ 28\qquad\textbf{(D)}\ 32\qquad\textbf{(E)}\ 40$

2019 AMC 10, 5

Tags: geometry , geometric transformation , reflection , AMC , AMC 10 , AMC 10 B , analytic geometry

Triangle $ABC$ lies in the first quadrant. Points $A$, $B$, and $C$ are reflected across the line $y=x$ to points $A'$, $B'$, and $C'$, respectively. Assume that none of the vertices of the triangle lie on the line $y=x$. Which of the following statements is [u][i]not[/i][/u] always true? $(A)$ Triangle $A'B'C'$ lies in the first quadrant. $(B)$ Triangles $ABC$ and $A'B'C'$ have the same area. $(C)$ The slope of line $AA'$ is $-1$. $(D)$ The slopes of lines $AA'$ and $CC'$ are the same. $(E)$ Lines $AB$ and $A'B'$ are perpendicular to each other.

2014 AMC 10, 4

Tags: symmetry , AMC 10 , AMC

Walking down Jane Street, Ralph passed four houses in a row, each painted a different color. He passed the orange house before the red house, and he passed the blue house before the yellow house. The blue house was not next to the yellow house. How many orderings of the colored houses are possible? ${ \textbf{(A)}\ 2\qquad\textbf{(B)}\ 3\qquad\textbf{(C)}\ 4\qquad\textbf{(D)}}\ 5\qquad\textbf{(E)}\ 6$

2024 AMC 10, 23

Tags: AMC , AMC 10 , AMC 12 , 2024 AMC , 2024 AMC 10b , 2024 AMC 12B

The Fibonacci numbers are defined by $F_1=1,$ $F_2=1,$ and $F_n=F_{n-1}+F_{n-2}$ for $n\geq 3.$ What is $$\dfrac{F_2}{F_1}+\dfrac{F_4}{F_2}+\dfrac{F_6}{F_3}+\cdots+\dfrac{F_{20}}{F_{10}}?$$ $\textbf{(A) }318 \qquad\textbf{(B) }319\qquad\textbf{(C) }320\qquad\textbf{(D) }321\qquad\textbf{(E) }322$

2023 AMC 10, 8

Tags: AMC , AMC 10 , AMC 10 A

Barb the baker creates a new temperature system for baking bread, Breadus, which is linearly based on Fahrenheit. Bread rises at $110$ F$^\circ$, which is $0$ on the Breadus scale. Bread bakes at $350$ F$^\circ$, which is $100$ on the Breadus scale. Bread is done when it’s internal temperature is $200$ F$^\circ.$ What is this temperature on the Breadus scale? $\textbf{(A) }33\qquad\textbf{(B) }34.5\qquad\textbf{(C) }36\qquad\textbf{(D) }37.5\qquad\textbf{(E) }39$