MathDB

p1. Hitori is trying to guess a three-digit integer with three different digits in five guesses to win a new guitar. She guesses

819

, and is told that exactly one of the digits in her guess is in the answer, but it is in the wrong place. Next, she guesses

217

, and is told that exactly one of the digits is in the winning number, and it is in the right place. After that, she guesses

362

, and is told that exactly two of the digits are in the winning number, and exactly one of them is in the right place. Then, she guesses

135

, and is told that none of the digits are in the winning number. Finally, she guesses correctly. What is the winning number?
p2. A three-digit integer

\overline{A2C}

, where

A

and

C

are digits, not necessarily distinct, and

A \ne 0

, is toxic if it is a multiple of

9

. For example,

126

is toxic because

126 = 9 \cdot 14

. Find the sum of all toxic integers.
p3. Cat and Claire are having a conversation about Cat’s favorite number. Cat says, “My favorite number is a two-digit multiple of

13

.” Claire asks, “Is there a two-digit multiple of

13

greater than or equal to your favorite number such that if you averaged it with your favorite number, and told me the result, I could determine your favorite number?” Cat says, “Yes. However, without knowing that, if I selected a digit of the sum of the squares of the digits of my number at random and told it to you, you would always be unable to determine my favorite number.” Claire says, “Now I know your favorite number!” What is Cat’s favorite number?
p4. Define

f(x) = \log_x(2x)

for positive

x

. Compute the product

f(4)f(8)f(16)f(32)f(64)f(128)f(256)f(512)f(1024)f(2048).

p5. Isosceles trapezoid

ABCD

has bases of length

AB = 4

and

CD = 8

, and height

6

. Let

F

be the midpoint of side

\overline{CD}

. Base

\overline{AB}

is extended past

B

to point

E

so that

\overline{BE} \perp \overline{EC}

. Also, let

\overline{DE}

intersect

\overline{AF}

G

\overline{BF}

H

, and

\overline{BC}

I

. If

[DFG] + [CFHI] - [AGHB] = \frac{m}{n}

where

m

and

n

are relatively prime positive integers, find

m + n

.
p6. Julia writes down all two-digit numbers that can be expressed as the sum of two (not necessarily distinct) positive cubes. For each such number

\overline{AB}

, she plots the point

(A,B)

on the coordinate plane. She realizes that four of the points form a rhombus. Find the area of this rhombus.
p7. When

(x^3 + x + 1)^{24}

is expanded and like terms are combined, what is the sum of the exponents of the terms with an odd coefficient?
p8. Given that

3^{2023} = 164550... 827

has

966

digits, find the number of integers

0 \le a \le 2023

such that

3^a

has a leftmost digit of

9

.
p9. Triangle

ABC

has circumcircle

\Omega

. Let the angle bisectors of

\angle CAB

and

\angle CBA

meet

\Omega

again at

D

and

E

. Given that

AB = 4

BC = 5

, and

AC = 6

, find the product of the side lengths of pentagon

BAECD

.
p10. Let

a_1, a_2, a_3, ...

be a sequence of real numbers and

\ell

be a positive real number such that for all positive integers

k

a_k = a_{k+28}

and

a_k + \frac{1}{a_{k+1}} = \ell

. If the sequence

a_n

is not constant, find the number of possible values of

\ell

.
p11. The numbers

3

6

9

, and

12

(or, in binary,

11

110

1001

1100

) form an arithmetic sequence of length four, and each number has exactly two 1s when written in base

2

. If the longest (nonconstant) arithmetic sequence such that each number in the sequence has exactly ten 1s when written in base

2

has length

n

, and the sequence with smallest starting term is

a_1

a_2

...

a_n

, find

n + a_2

.
p12. Let

x, y, z

be real numbers greater than 1 that satisfy the inequality

\log_{\sqrt{x^{12}y^8z^9}}\left( x^{\log x}y^{\log y}z^{\log z} \right) \le 4,

where

\log (x)

denotes the base

10

logarithm. If the maximum value of

\log \left(\sqrt{x^5y^3z} \right)

can be expressed as

\frac{a+b\sqrt{c}}{d}

, where

a, b, c, d

are positive integers such that

c

is square-free and

gcd(a, b, d) = 1

, find

a + b + c + d

.
PS. You should use hide for answers. Collected [url=https://artofproblemsolving.com/community/c5h2760506p24143309]here.

Problem Statement