Winner2013 wrote:Committee X and Committee Y , which have no common members, will combine to form Committee Z. Does Committee X have more members than Committee Y?
(1) The average (arithmetic mean) age of the members of Committee X is 25.7 years and the
average age of the members of Committee Y is 29.3 years.
(2) The average (arithmetic mean) age of the members of Committee Z will be 26.6 years.
Target question: Does Committee X have more members than Committee Y?
Statement 1: The average (arithmetic mean) age of the members of Committee X is 25.7 years and the average age of the members of Committee Y is 29.3 years.
No way to determine which committee has more people.
Since we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: The average (arithmetic mean) age of the members of Committee Z will be 26.6 years.
No way to determine which committee has more people.
Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined
IMPORTANT CONCEPT:
If there are 2 populations (A and B) and A's population is greater than B's population, then the average for the COMBINED population will be closer to A's average than to B's average.
Committee X has an average age of 25.7 years
Committee Y has an average age of 29.3 years
If the two committees had the
same population, then the combined committee (Z) would have an average age of 27.5
[since (25.7 + 29.3)/2 = 27.5]
In actuality, the COMBINED committee has an average age of 26.6 years. Since 26.6 is closer to 25.7 (committee X's average) than to 29.3 (committee Y's average), we can conclude that
committee X must have more people
Since we can answer the
target question with certainty, the combined statements are SUFFICIENT
Aside: for more information on weighted averages, you can watch this free GMAT Prep Now video: https://www.gmatprepnow.com/module/gmat- ... ics?id=805
Answer =
C
Cheers,
Brent
