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MathNet 2022-part-02 — 197 problems (EN–VI) Question 47

Math Olympiad Vault · MathNet 2022-part-02 — 197 problems (EN–VI)

Question 47

A fly farm contains $100001$ fruit flies. A research group wishes to buy some flies from the farm to perform (once) either experiment A or experiment B (but not both).

For experiment A, the research group needs a set of flies in which no fly is a descendant of any other. For such a set, the research group would pay the farm $505$ euros plus $5$ euros per fly bought.

For experiment B, the research group needs a set of flies in which among every two flies, one is a descendant of the other. For such a set, the research group would pay the farm $1000$ euros plus $10$ euros per fly bought.

Prove that there exists a set of flies in the farm for which the research group would pay at least $3010$ euros.