Problem

Source: (2021-) 2022 XV 15th Dürer Math Competition Finals Day 2 E15

Tags: combinatorics



Doofy duck buy tangerines in the store. All tangerines have equal weight and are divided into $9$, $10$, $11$, $12$, or $13$ equal wedges, although this cannot be seen without peeling them. How many tangerines does Doofy duck need to buy if he wishes to eat exactly one tangerine’s worth while eating at most one wedge from every tangerine? Doofy duck only peels the tangerines at home.