Probability question

[kthom83]

[Kthom83-"If it doesn't rain on Saturday, then the events are independent."-Incorrect.Whatever happens on Sunday is conditional to what happens on Saturday, otherwise, refer to my earlier post, the problem becomes trivial!

I don't agree. Question doesn't state that. That is an assumption, which you are making. If that were the case, question doesn't have to state "Rain on Saturday" case explicitly.

[jsummers]

I agree with kthom83. Question doesn't say that. Infact, I feel the combination of dependency and independency would only make this question sense.

[shaji]

"Infact, I feel the combination of dependency and independency would only make this question sense" Logic is flawed and not allowed in mathematics.

"That is an assumption, which you are making. If that were the case, question doesn't have to state "Rain on Saturday" case explicitly.". I repeat its an inference, maths leaves no room for assumptions. Even the question setter didn't consider the trivial condition in the answer choices.

[jsummers]

"Infact, I feel the combination of dependency and independency would only make this question sense" Logic is flawed and not allowed in mathematics.

"That is an assumption, which you are making. If that were the case, question doesn't have to state "Rain on Saturday" case explicitly.". I repeat its an inference, maths leaves no room for assumptions. Even the question setter didn't consider the trivial condition in the answer choices.

I didn't assume anything. I just used exact information mentioned in the question. Question didn't say that P(Saturday no rain) has any impact on Sunday. Therefore, P(Sunday Rain) when there is no rain on Saturday will remain as .6. Period.

As it is not a GMAT question, I don't care what the choices are. I have seen several questions that are incorrect (some of them are posted in this form, which Instructors agree that they are incorrect). If the correct answer given is anything other than .84, I would throw this question into trash.

[shaji]

"Question didn't say that P(Saturday no rain) has any impact on Sunday." The question says that rain on previous day affects chances to rain on the following day. The converse is an obvious conclusion!!. Without this conclusion, the problem looses its essence and becomes trivial. "Therefore, P(Sunday Rain) when there is no rain on Saturday will remain as .6. Period." This is the precise trap, you building for yourself, since even the questionsetter thought it not worthwhile considering!!

"As it is not a GMAT question, I don't care what the choices are" ; ..If the correct answer given is anything other than .84, I would throw this question into trash.". You may do so at your own peril!! Since it's not GMAT, is preposterous to consider all answer choices are incorrect. Let me caution you variants of this same problem could be a GMAT problem.

Having a General Math Forum for non GMAT Prep Problems are meaningless for those who are naive NOT TO CARE for the answer choices even if one of the answers are correct and based on math logic.

[tim]

Yeah, this problem goes in the trash. Most of what you all are discussing revolves around your different approaches to interpreting what is, at its heart, an ambiguous and awkwardly-worded question. I can come up with several different interpretations (and hence several different answers) for this one, which is why it's invalid. Don't worry though - actual GMAT questions are not going to have these kinds of problems. Let this one go, and focus on problems that are actually going to build your GMAT skills.. :)

[shaji]

Yeah, this problem goes in the trash. Most of what you all are discussing revolves around your different approaches to interpreting what is, at its heart, an ambiguous and awkwardly-worded question. I can come up with several different interpretations (and hence several different answers) for this one, which is why it's invalid. Don't worry though - actual GMAT questions are not going to have these kinds of problems. Let this one go, and focus on problems that are actually going to build your GMAT skills.. :)

Its a pity that this problem is 'trashed' in such an off-hand manner.It's a problem that has considerable practical significance. It tests a concept of conditional probability that managers face on a day to day basis. The GMAT tests Management aptitiude and its quite fit to have such concepts tested, which will go a long way to seperate the grain from the chaff. Certainly the GMAT is evolving and that for the better to aid Management Institutions to choose the best and produce better managers.

[tim]

The problem is invalid. It has no solution. That's why we trash it. Conditional probability is very important, yes, but this problem does not do the concept justice and should be avoided..

[shaji]

The problem is invalid. It has no solution. That's why we trash it. Conditional probability is very important, yes, but this problem does not do the concept justice and should be avoided..

The problem could have been worded better. Nevertheless, its better 'justice' to explore the concept of conditional probability in the problem as I have in my posts above than 'trash' it. Perhaps, 'injustice' to just 'trash' it.

[tim]

No. This is not true. It is in fact NOT productive to discuss a problem so inherently flawed that it has no solution. If you wish to discuss conditional probability separately from this question, I encourage you to start a conditional probability thread. It is definitely a good topic to explore, but this particular problem is not worth exploring any further..