when the exercise says bag 2, the correct numbers are 5 smooth and 2
rough, that's why I calculated 5/7 as a probability. Sorry for the
confusion (extra)
-------- Mensaje original --------
Asunto: confuse exercise
Fecha: Tue, 08 Dec 2009 15:09:22 -0600
De: Rodrigo Briceño <[log in to unmask]>
Responder a: [log in to unmask]
Organización: Sanigest
Para: [log in to unmask]
Dear colisters. I took the time to solve an exercise from a textbook,
but I suddenly lost the perspective of what is really asking the third
item on it. The exercise reads:
Three identical bags contain crystall balls. The first one has 6 smooth
ones and 4 rough ones; the second has three smooth and 2 rough and the
third has 4 smooth and 7 rough. Determine:
1. The probability that when extracting randomly one ball this is rough.
Answer:
P(Smooth)=1/3*6/10 + 1/3*5/7 + 1/3*4/11=0.56
P(Rough)=0.44
2. An extraction was made and the ball was smooth. What is the
probability that the bag 1 had been selected?
This is a bayes one: (1/3*6/10)/0.56 = 0.36
And the confusing (for me) one:
3. In the previous extraction the ball fall and broke. What are the
probabilities that a new randomly extraction the ball will be rough? The
answer of the book says 0.49, but what I did gave me 0.46
My try was: 1/3*5/9+1/3*5/7+1/3*4/11= 0.46, since the only change is
that the first bag will have only 9 balls (one smooth less).
Anybody has an alternative opinion?
Thanks
--
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__________________________________________________________________
*Rodrigo Briceño*
Project Manager
Sanigest Internacional
+506 22-91-12-00 ext. 113 * Oficina* *Costa Rica*
+506 22-32-08-30 *Fax
*[log in to unmask] <mailto:[log in to unmask]>
_www.sanigest.com_ <http://www.sanigest.com/>
MSN: [log in to unmask] <mailto:[log in to unmask]>
SKYPE: rbriceno1087
_____________________
This communication contains legal information which is privileged and
confidential. It is for the exclusive use of the address and
distribution, dissemination, copying or use by others is strictly
prohibited. If you have received this communication by error, please
delete the original message and e-mail us.
Esta comunicación contiene información legal privilegiada y confidencial
para el uso exclusivo del destinatario. La distribución, diseminación,
copia u otro uso por terceras personas es estrictamente prohibida. Si
usted ha recibido esta comunicación por error, le rogamos borrar el
mensaje original y comunicárnoslo a esta misma dirección.
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