MathDB

[hide=D stands for Descartes, L stands for Leibniz]they had two problem sets under those two names
Set 1
D.1 / L.1 Find the units digit of

3^{1^{3^{3^7}}}

.
D.2 Find the positive solution to the equation

x^3 - x^2 = x - 1

.
D.3 Points

A

and

B

lie on a unit circle centered at O and are distance

1

apart. What is the degree measure of

\angle AOB

?
D.4 A number is a perfect square if it is equal to an integer multiplied by itself. How many perfect squares are there between

1

and

2019

, inclusive?
D.5 Ted has four children of ages

10

12

15

, and

17

. In fifteen years, the sum of the ages of his children will be twice Ted’s age in fifteen years. How old is Ted now?
Set 2
D.6 Mr. Schwartz is on the show Wipeout, and is standing on the first of

5

balls, all in a row. To reach the finish, he has to jump onto each of the balls and collect the prize on the final ball. The probability that he makes a jump from a ball to the next is

1/2

, and if he doesn’t make the jump he will wipe out and no longer be able to finish. Find the probability that he will finish.
D.7 / L. 5 Kevin has written

5

MBMT questions. The shortest question is

5

words long, and every other question has exactly twice as many words as a different question. Given that no two questions have the same number of words, how many words long is the longest question?
D.8 / L. 3 Square

ABCD

with side length

1

is rolled into a cylinder by attaching side

AD

to side

BC

. What is the volume of that cylinder?
D.9 / L.4 Haydn is selling pies to Grace. He has

4

pumpkin pies,

3

apple pies, and

1

blueberry pie. If Grace wants

3

pies, how many different pie orders can she have?
D.10 Daniel has enough dough to make

8

12

-inch pizzas and

12

8

-inch pizzas. However, he only wants to make

10

-inch pizzas. At most how many

10

-inch pizzas can he make?
Set 3
D.11 / L.2 A standard deck of cards contains

13

cards of each suit (clubs, diamonds, hearts, and spades). After drawing

51

cards from a randomly ordered deck, what is the probability that you have drawn an odd number of clubs?
D.12 / L. 7 Let

s(n)

be the sum of the digits of

n

. Let

g(n)

be the number of times s must be applied to n until it has only

1

digit. Find the smallest n greater than

2019

such that

g(n) \ne g(n + 1)

.
D.13 / L. 8 In the Montgomery Blair Meterology Tournament, individuals are ranked (without ties) in ten categories. Their overall score is their average rank, and the person with the lowest overall score wins. Alice, one of the

2019

contestants, is secretly told that her score is

S

. Based on this information, she deduces that she has won first place, without tying with anyone. What is the maximum possible value of

S

?
D.14 / L. 9 Let

A

and

B

be opposite vertices on a cube with side length

1

, and let

X

be a point on that cube. Given that the distance along the surface of the cube from

A

X

1

, find the maximum possible distance along the surface of the cube from

B

X

.
D.15 A function

f

with

f(2) > 0

satisfies the identity

f(ab) = f(a) + f(b)

for all

a, b > 0

. Compute

\frac{f(2^{2019})}{f(23)}

.

PS. You should use hide for answers. D.1-15 / L1-9 problems have been collected [url=https://artofproblemsolving.com/community/c3h2790795p24541357]here and L10,16-30 [url=https://artofproblemsolving.com/community/c3h2790825p24541816]here. Collected [url=https://artofproblemsolving.com/community/c5h2760506p24143309]here.

Problem Statement