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Numbered Balls Drawing Probability

1425ApprenticeCombinatoricsProbability

UNIONE MATEMATICA ITALIANA SCUOLA NORMALE SUPERIORE DI PISA Progetto Olimpiadi di Matematica

In una scatola ci sono venti palline numerate da 1 a 20. Ciascun numero è presente in una e una sola di queste palline. Quante palline diverse dobbiamo estrarre come minimo, per essere sicuri che il prodotto dei loro numeri sia un multiplo di 12? (A) 7 (B) 11 (C) 12 (D) 15 (E) 18.
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