CR 1000

Expert replies

f2001290: Master | Next Rank: 500 Posts; Posts: 400; Joined: Sat Mar 10, 2007 4:04 amFollowed by: 1 member; Thanked: 1 times

by f2001290 » Sun Jun 03, 2007 9:26 am

A low-pressure weather system is approaching Plainville; rainfall results from about 70 percent of such systems in the Plainville area. Moreover, the current season, spring, is the time of year in which thundershowers, which sometimes result from low-pressure systems, are most likely to occur in Plainville.
Knowing which one of the following, in addition to the information above, would be most useful for determining the probability that Plainville will have a thundershower soon?
(A) the percentage of thundershowers in Plainville that occur in the spring
(B) the percentage of spring rainfalls in Plainville that are thundershowers
(C) the percentage of thundershowers in Plainville that result from low-pressure systems
(D) whether low-pressure systems in other areas are associated with rainfall
(E) whether Plainville has more or fewer thundershowers each spring than do nearby towns

Source: Beat The GMAT — Critical Reasoning | Sun Jun 03, 2007 9:26 am

Maciek: Master | Next Rank: 500 Posts; Posts: 164; Joined: Sun Jul 18, 2010 5:26 amFollowed by: 4 members; Thanked: 49 times; GMAT Score:710

by Maciek » Sat Aug 28, 2010 1:04 am

Hi all!

I've found lost CR question.

IMO B

The probability of something being the case given that something else is the
case is called a conditional probability. We express the conditional probability
of A on B by writing Pr(A\B).

Source: Critical reasoning user manual

Pr(rainfall\low-pressure weather system) = 70%

(A) it is irrelevant

(B) it is most useful for determining the requested probability

(C) it is out of scope because spring is the time of year in which thundershowers are most likely to occur in Plainville

(D) it is out of scope because of other areas

(E) it is out of scope

hope it helps!

If you don't agree with my reasoning, post here! Thanks!

Best,
Maciek

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scholardream: Senior | Next Rank: 100 Posts; Posts: 83; Joined: Fri May 06, 2011 9:08 am; Thanked: 5 times; GMAT Score:610

by scholardream » Wed May 02, 2012 9:52 am

Hi Maciek,
I don't understand why C is out of scope, as thundershowers, which sometimes result from low-pressure systems and we have premise that A low-pressure weather system is approaching Plainville, therefore if we know C, we could determine the probability that Plainville will have a thundershower.

spartacus1412: Master | Next Rank: 500 Posts; Posts: 110; Joined: Wed Feb 22, 2012 11:28 pmFollowed by: 1 member; Location: India; Thanked: 13 times

by spartacus1412 » Thu May 03, 2012 5:45 am

I agree with scholardream.. I would Prefer C

Its do or die this time!
Practise, practise and practise.

ice_rush: Master | Next Rank: 500 Posts; Posts: 341; Joined: Sun Mar 25, 2012 6:59 pmFollowed by: 4 members; Thanked: 17 times; GMAT Score:720

by ice_rush » Thu May 03, 2012 12:35 pm

agreed - the answer should be (B). tricky question.

heymayank08: Master | Next Rank: 500 Posts; Posts: 181; Joined: Fri Feb 17, 2012 9:36 amFollowed by: 1 member; Thanked: 1 times; GMAT Score:620

by heymayank08 » Sun May 06, 2012 7:04 pm

spartacus1412 wrote:I agree with scholardream.. I would Prefer C

+1 C pls explain why is it out of scope..

ice_rush: Master | Next Rank: 500 Posts; Posts: 341; Joined: Sun Mar 25, 2012 6:59 pmFollowed by: 4 members; Thanked: 17 times; GMAT Score:720

by ice_rush » Sun May 06, 2012 7:40 pm

We know that thundershowers are most likely to occur in spring. So whether thundershowers result from low-pressure systems or NOT does not help us in determining the likelihood of thundershowers. Also, choice (C) does not mention anything about thundershowers in spring. We need an answer that ties rainfall to thundershowers and only choice (B) does that.

hope this helps

confuse mind: Master | Next Rank: 500 Posts; Posts: 462; Joined: Wed Jan 19, 2011 1:08 pmFollowed by: 4 members; Thanked: 10 times

by confuse mind » Wed May 09, 2012 8:53 pm

I will go for A since this is exactly what is asked in the question.
The information given in the stimulus is not used if I go with option A, and I feel it has been given to mislead.

B - the percentage of spring rainfalls in Plainville that are thundershowers
there can be a thundershower without rainfall as well. Secondly, there can be rainfall for reasons other than low-pressure and thus it cannot give correct probability or rather will give less probability than the correct

C - the percentage of thundershowers in Plainville that result from low-pressure systems
thundershowers can result from reasons other than low-pressure and not sufficient to calculate the probability

@Experts...help please

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