MathDB
friendships among 26 people, May Olympiad (Olimpiada de Mayo) 2015 L1 P5

Source:

September 26, 2021
combinatorics

Problem Statement

Twenty-six people gather in a house. Alicia is friends with only one person, Bruno is friends with two people, Carlos is a friend of three, Daniel is four, Elías is five, and so following each person is friend of a person more than the previous person, until reaching Yvonne, the person number twenty-five, who is a friend to everyone. How many people is Zoila a friend of, person number twenty-six?
Clarification: If AA is a friend of BB then BB is a friend of AA.