卡住了..哪位点拨一下吧 -在线等

zzzandy · 发表于 2009-1-17 20:45:00

PREP题

6. What is the average (arithmetic mean) height of the n people in a certain group?

1) The average height of the (n/3) tallest people in the group is 6 feet (2 1/2) inches and the average height of the rest of the people in the group is 5 feet 10 inches;

2) The sum of the height of the n people is 178 feet 9 inches.

Answer is A.

条件2为什么不对?

cageshi117 · 发表于 2009-1-17 21:07:00

The sum of the height of the n people is 178 feet 9 inches.

We have konwn the sum but we still can't get how many people (n)there are in a certain group,so what's the average?===>2 is not suffisant

zzzandy · 发表于 2009-1-17 21:18:00

if "n" is not how many people, how is n/3 in "condition 1"

cageshi117 · 发表于 2009-1-17 21:28:00

but we can see that the ratio between tallest people and the rest is 1:2 so we don't have to use N

lavajak · 发表于 2009-1-17 21:44:00

(6.2 x 2/3 x n + 5.1 x 1/3 x n) / n, 约分了, n is not necessarily to be known.

zzzandy · 发表于 2009-1-17 21:50:00

solved !!THANKS lavajak & cageshi117

卡住了..哪位点拨一下吧 -在线等

卡住了..哪位点拨一下吧 -在线等

所属分类: GMAT考试

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