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Part of 2007 Portugal MO

Problems(1)

necklace with 20 pearls, blue and white

Source: Portugal OPM 2007 p1

5/19/2024
Joao had blue, white and red pearls and with them he made a necklace with 2020 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?
combinatorics