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Difference between revisions of "2020 AIME II Problems"

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==Problem 6==
 
==Problem 6==
  
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Define a sequence recursively by <math>t_1 = 20</math>, <math>t_2 = 21</math>, and<cmath>t_n = \frac{5t_{n-1}+1}{25t_{n-2}}</cmath>for all <math>n \ge 3</math>. Then <math>t_{2020}</math> can be written as <math>\frac{p}{q}</math>, where <math>p</math> and <math>q</math> are relatively prime positive integers. Find <math>p+q</math>.
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[[2020 AIME II Problems/Problem 6 | Solution]]
 
[[2020 AIME II Problems/Problem 6 | Solution]]

Revision as of 12:58, 14 December 2020

2020 AIME II (Answer Key)
Printable version | AoPS Contest Collections • PDF

Instructions

  1. This is a 15-question, 3-hour examination. All answers are integers ranging from $000$ to $999$, inclusive. Your score will be the number of correct answers; i.e., there is neither partial credit nor a penalty for wrong answers.
  2. No aids other than scratch paper, graph paper, ruler, compass, and protractor are permitted. In particular, calculators and computers are not permitted.
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15

Problem 1

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Solution

Problem 2

Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks!

Solution

Problem 3

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Problem 4

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Solution

Problem 5

Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks! Scorpio Sucks!

Solution

Problem 6

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Solution

Problem 7

Two congruent right circular cones each with base radius $3$ and height $8$ have axes of symmetry that intersect at right angles at a point in the interior of the cones a distance $3$ from the base of each cone. A sphere with radius $r$ lies within both cones. The maximum possible value of $r^2$ is $\frac{m}{n}$, where $m$ and $n$ are relatively prime positive integers. Find $m+n$.

Solution

Problem 8

Define a sequence recursively by $f_1(x)=|x-1|$ and $f_n(x)=f_{n-1}(|x-n|)$ for integers $n>1$. Find the least value of $n$ such that the sum of the zeros of $f_n$ exceeds $500,000$.

Solution

Problem 9

While watching a show, Ayako, Billy, Carlos, Dahlia, Ehuang, and Frank sat in that order in a row of six chairs. During the break, they went to the kitchen for a snack. When they came back, they sat on those six chairs in such a way that if two of them sat next to each other before the break, then they did not sit next to each other after the break. Find the number of possible seating orders they could have chosen after the break.

Solution

Problem 10

Find the sum of all positive integers $n$ such that when $1^3+2^3+3^3+\cdots +n^3$ is divided by $n+5$, the remainder is $17$.

Solution

Problem 11

Let $P(x) = x^2 - 3x - 7$, and let $Q(x)$ and $R(x)$ be two quadratic polynomials also with the coefficient of $x^2$ equal to $1$. David computes each of the three sums $P + Q$, $P + R$, and $Q + R$ and is surprised to find that each pair of these sums has a common root, and these three common roots are distinct. If $Q(0) = 2$, then $R(0) = \frac{m}{n}$, where $m$ and $n$ are relatively prime positive integers. Find $m + n$.

Solution

Problem 12

Let $m$ and $n$ be odd integers greater than $1.$ An $m\times n$ rectangle is made up of unit squares where the squares in the top row are numbered left to right with the integers $1$ through $n$, those in the second row are numbered left to right with the integers $n + 1$ through $2n$, and so on. Square $200$ is in the top row, and square $2000$ is in the bottom row. Find the number of ordered pairs $(m,n)$ of odd integers greater than $1$ with the property that, in the $m\times n$ rectangle, the line through the centers of squares $200$ and $2000$ intersects the interior of square $1099$.

Solution

Problem 13

Convex pentagon $ABCDE$ has side lengths $AB=5$, $BC=CD=DE=6$, and $EA=7$. Moreover, the pentagon has an inscribed circle (a circle tangent to each side of the pentagon). Find the area of $ABCDE$.

Solution

Problem 14

For real number $x$ let $\lfloor x\rfloor$ be the greatest integer less than or equal to $x$, and define $\{x\} = x - \lfloor x \rfloor$ to be the fractional part of $x$. For example, $\{3\} = 0$ and $\{4.56\} = 0.56$. Define $f(x)=x\{x\}$, and let $N$ be the number of real-valued solutions to the equation $f(f(f(x)))=17$ for $0\leq x\leq 2020$. Find the remainder when $N$ is divided by $1000$.

Solution

Problem 15

Let $\triangle ABC$ be an acute scalene triangle with circumcircle $\omega$. The tangents to $\omega$ at $B$ and $C$ intersect at $T$. Let $X$ and $Y$ be the projections of $T$ onto lines $AB$ and $AC$, respectively. Suppose $BT = CT = 16$, $BC = 22$, and $TX^2 + TY^2 + XY^2 = 1143$. Find $XY^2$.

Solution

2020 AIME II (Problems • Answer Key • Resources)
Preceded by
2020 AIME I Problems 		Followed by
2021 AIME I Problems
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