necklace with 20 pearls, blue and white
Source: Portugal OPM 2007 p1
May 19, 2024
combinatorics
Problem Statement
Joao had blue, white and red pearls and with them he made a necklace with pearls that has as many blue as white pearls. João noticed that, regardless of how he cut the necklace into two parts, both with an even number of pearls, one of the parts would always have more blue pearls than white ones. How many red pearls are in Joao's necklace?