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10 Jun 2015, 04:15
Kudos
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
87% (01:34) correct
13%
(01:55)
wrong
based on 345
sessions
History
Date
Time
Result
Not Attempted Yet
What is the average of 12, 13, 14, 510, 520, 530, 1,115, 1,120, and 1,125?
(A) 419
(B) 551
(C) 601
(D) 620
(E) 721
Kudos for a correct solution.
(A) 419
(B) 551
(C) 601
(D) 620
(E) 721
Kudos for a correct solution.
10 Jun 2015, 08:58
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Bunuel
looking at the set of numbers ,we may save time to make use of the numbers..
13 is avg of first three numbers , 520 for next three and 1120 for last three..
so basically we have to find avg of these three numbers..
551 ans ..B.. we dont require to get into proper calculation .. total >1600.. ans has to be between 500 and 600..only B remains
15 Jun 2015, 01:35
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Bunuel
MANHATTAN GMAT OFFICIAL SOLUTION:
The simple average formula (Average = Sum/Number of terms) applies to this problem.
However, the chance of computational error is high on a problem with this many terms of such a large size.
A nice shortcut is possible if we group the similar terms:
Group A: 12, 13, 14 (equidistant terms with an average of 13, the middle term)
Group B: 510, 520, 530 (equidistant terms with an average of 520, the middle term)
Group C: 1,115, 1,120, 1,125 (equidistant terms with an average of 1,120, the middle term)
Since each group of terms consisted of three values (and thus were equally weighted in the set of
Since each group of terms consisted of three values (and thus were equally weighted in the set of nine terms), the average of all nine original terms is simply the average of the respective averages of Groups A, B, and C:
13 + 520 + 1,120 = 1,653.
Average = 1,653/3 = 551
The correct answer is B.
