MathDB
2019 Girls in Math at Yale - Individual Round

Source:

September 30, 2023
Yalealgebrageometrycombinatoricsnumber theory

Problem Statement

p1. Hannah is training for a marathon. This week, she ran 5050 miles. In each of the next 88 weeks, she plans on running 55 miles more than in the previous week. How many total miles will she run over the course of her 9 weeks of training?
p2. An ant is standing at the bottom left corner of a 33 by 33 grid. How many ways can it get to the top right corner if it can only move up, right, and left, and it is not allowed to cross the same edge twice? https://cdn.artofproblemsolving.com/attachments/8/b/a28d64f3c14388cda81a603c0073ca60f91226.png
p3. If 5656 is 35%35\% of x, what is 55%55\% of xx?
p4. Diana covers a large square of area 3636 with six non-overlapping smaller squares (which can have different sizes). What is the area of the largest of these six smaller squares?
p5. Find the largest value of xx satisfying x2+2x15=x2+6x9|x^2 + 2x - 15| = |x^2 + 6x - 9|.
p6. In the diagram below, all seven of the small rectangles are congruent. If the perimeter of the large rectangle is 6565, what is its area? https://cdn.artofproblemsolving.com/attachments/6/1/ccdac7ac6196f43ccfe91c3f117ce2439b4919.png
p7. Find the value of xx that satisfies x5107+x7105+x9103+x11101=x1044+x1082\frac{x-5}{107}+\frac{x - 7}{105}+\frac{x - 9}{103}+\frac{x - 11}{101}= \frac{x - 104}{4}+\frac{x - 108}{2}
p8. Let ABC\vartriangle ABC be a right triangle with hypotenuse AC\overline{AC}. Construct three squares: one with AB\overline{AB} as a side, one with AC\overline{AC} as a side, and one with BC\overline{BC} as a side. Inscribe a circle in each of the three squares. The area of the circle that is tangent to AB\overline{AB} is 1818, and the area of the circle that is tangent to BC\overline{BC} is 2424. What is the area of the circle that is tangent to AC\overline{AC}?
p9. Emma checks her email at least once every day but no more than 1010 times in any 33 consecutive days. If she checked her email 2525 times over the course of last week (77 consecutive days), what is the largest number of times she could have checked it on the second day of last week?
p10. 1212 balls labeled with the integers 11 through 1212, are placed in a box. Alexandra randomly takes out 33 of them, sets aside the largest, and repeats this procedure (without replacement) until there are no balls left in the box. What is the probability that the 44 balls set aside are labeled 99, 1010, 1111, and 1212?
p11. Let xx be the largest real number that can be expressed as 1a+1b+1c\dfrac{1}{a+\dfrac{1}{b+\dfrac{1}{c}}} , where aa, bb, and c are all real numbers (not necessarily distinct) between 11 and 1010 (inclusive). Similarly, let yy be the smallest real number that can be expressed in the same way. Find xyx - y.
p12. Daisy finds a chalkboard with the number 44 on it. She may write more numbers on the chalkboard as follows: if any number x is on the chalkboard, she may write x+3x + 3 and/or x2+2x^2 + 2, and she may repeat this process as many times as she wants. What is the largest whole number that Daisy is not able to write on the chalkboard?
PS. You should use hide for answers. Collected [url=https://artofproblemsolving.com/community/c5h2760506p24143309]here.