MathDB
Girls in Math at Yale 2022 Mathathon Round 4

Source:

March 7, 2022
logarithmsalgebrageometrycombinatoricsnumber theoryYale

Problem Statement

p10 Kathy has two positive real numbers, aa and bb. She mistakenly writes log(a+b)=log(a)+log(b),\log (a + b) = \log (a) + \log( b), but miraculously, she finds that for her combination of aa and bb, the equality holds. If a=2022ba = 2022b, then b=pqb = \frac{p}{q} , for positive integers p,qp, q where gcd(p,q)=1gcd(p, q) = 1. Find p+qp + q.
p11 Points XX and YY lie on sides ABAB and BCBC of triangle ABCABC, respectively. Ray XY\overrightarrow{XY} is extended to point ZZ such that A,CA, C, and ZZ are collinear, in that order. If triangleABZ ABZ is isosceles and triangle CYZCYZ is equilateral, then the possible values of ZXB\angle ZXB lie in the interval I=(ao,bo)I = (a^o, b^o), such that 0a,b3600 \le a, b \le 360 and such that aa is as large as possible and bb is as small as possible. Find a+ba + b.
p12 Let S={(a,b)0a,b3,aS = \{(a, b) | 0 \le a, b \le 3, a and bb are integers }\}. In other words, SS is the set of points in the coordinate plane with integer coordinates between 00 and 33, inclusive. Prair selects four distinct points in SS, for each selected point, she draws lines with slope 11 and slope 1-1 passing through that point. Given that each point in SS lies on at least one line Prair drew, how many ways could she have selected those four points?