$[$ Mathematical logic (other).]

About mushrooms. In the basket, there are 30 mushrooms. Among any 12 of them, there is at least one russula, and among any 20 mushrooms, there is at least one boletus. How many russulas and how many boletuses are in the basket?

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Note: Among any 12 mushrooms, there is at least one russula.

## Solution

Since among any 12 mushrooms there is at least one russula, there cannot be more than 11 boletus mushrooms. And since among any 20 mushrooms there is at least one boletus, there cannot be more than 19 russulas. But since there are 30 mushrooms in total in the basket, the only possible option is that there are 19 russulas and 11 boletus mushrooms?