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Problemas.estimulantes.de.probabilidad.y.estadistica

Problemas.estimulantes.de.probabilidad.y.estadistica

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<strong>de</strong> pacientes que obtienen alivio. a) Encontrar la función <strong>de</strong> masa <strong>de</strong> <strong>probabilidad</strong> para X,suponiendo que la afirmación <strong>de</strong>l fabricante sea correcta.Solución.Denotamos por A=“el ácido es efectivo”. P (A) =0.9.· P (X =0)=P (Ā ∩ Ā ∩ Ā ∩ Ā) =P (Ā)4 =0.1 4 =0.0001.· P (X =1)== P [( A ∩ Ā ∩ Ā ∩ Ā) ∪ ( Ā ∩ A ∩ Ā ∩ Ā) ∪ ( Ā ∩ Ā ∩ A ∩ Ā) ∪ Ā ∩ Ā ∩ Ā ∩ A)] ==4P (Ā)3 P (A) =4· 0.1 3 · 0.9 =0.0036.· P (X =2)== P [ ( Ā ∩ Ā ∩ A ∩ A) ∪ ( Ā ∩ A ∩ Ā ∩ A) ∪ ( Ā ∩ A ∩ A ∩ Ā) ∪∪ ( A ∩ Ā ∩ Ā ∩ A) ∪ ( A ∩ Ā ∩ A ∩ Ā) ∪ (A ∩ A ∩ Ā ∩ Ā)] ==6· 0.1 2 · 0.9 2 =0.048 6.· P (X =3)== P [( A ∩ A ∩ A ∩ Ā) ∪ ( A ∩ A ∩ Ā ∩ A) ∪ ( A ∩ Ā ∩ A ∩ A) ∪ (Ā ∩ A ∩ A ∩ A)] ==4· 0.1 · 0.9 3 =0.2916.· P (X =4)=P (A ∩ A ∩ A ∩ A) =0.9 4 =0.6561.Comprobamos que 0.000 1 + 0.0036 + 0.0486 + 0.2916 + 0.6561 = 1.74 VARIABLES DISCRETAS

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