A question

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adilka: Senior | Next Rank: 100 Posts; Posts: 79; Joined: Thu Oct 23, 2008 9:28 am; Location: Canada; Thanked: 1 times; GMAT Score:700

by adilka » Fri Jan 16, 2009 3:25 pm

Peter, Paul, and Mary each received a passing score on his/her history midterm. The average (arithmetic mean) of the three scores was 78. What was the median of the three scores?

(1) Peter scored a 73 on his exam.

(2) Mary scored a 78 on her exam.

Source: Manhattan GMAT

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Source: Beat The GMAT — Data Sufficiency | Fri Jan 16, 2009 3:25 pm

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

Re: A question

by Ian Stewart » Fri Jan 16, 2009 11:14 pm

adilka wrote:Peter, Paul, and Mary each received a passing score on his/her history midterm. The average (arithmetic mean) of the three scores was 78. What was the median of the three scores?

(1) Peter scored a 73 on his exam.

(2) Mary scored a 78 on her exam.

Source: Manhattan GMAT

You'd never see a question worded quite like this on the real GMAT - after all, what's a 'passing score'? In the US, it would likely be 50%; here in the UK, it would normally be 40%. The GMAT doesn't test your knowledge of American cultural conventions.

Still, the answer should be B. The first statement is not sufficient; if Peter scored a 73, there are many possible values for the median (the median could be 73 if the other two scores were 70 and 91, for example, but could be 78 if the other two scores were 78 and 83).

The second statement is sufficient; if Mary scored a 78, and the mean score was 78, the other two scores must add to 156. One of them must be less than or equal to 156/2 = 78, the other greater than equal to 156/2 = 78, and 78 must be the median.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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adilka: Senior | Next Rank: 100 Posts; Posts: 79; Joined: Thu Oct 23, 2008 9:28 am; Location: Canada; Thanked: 1 times; GMAT Score:700

by adilka » Sat Jan 17, 2009 8:52 am

Correct, the answer is B.
To your point on the passing score. This information isnt really used to solve the question, so it's a distraction at best.

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