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GMAT 数学题(16)

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11#
发表于 2011-2-14 15:40:38 | 只看该作者
答案选E,2A(n)=13*(13+1), 所以A(n)=91,
        2 A(m)=12*(12+1)所以 A(m)=78
               B(p)=13^2=169
               A(n)+A(m)=91+78=169= B(p)
   这样对吧,自己做的,大家看看,仅供参考参考
12#
 楼主| 发表于 2011-2-14 21:30:31 | 只看该作者
LS is right.  The answer is E, 91.
13#
 楼主| 发表于 2011-2-14 21:37:25 | 只看该作者
The key is to realize that the sum of any consecutive A(n) and A(n+1) is a square number!!!

55+66 = 121
66+78 = 144
78+91 = 169
...
14#
发表于 2011-2-14 21:50:00 | 只看该作者
弱弱问一句,什么叫triangular numbers ?
15#
 楼主| 发表于 2011-2-15 08:00:36 | 只看该作者
弱弱问一句,什么叫triangular numbers ?
-- by 会员 neverlandlin (2011/2/14 21:50:00)



http://en.wikipedia.org/wiki/Triangular_number

A triangular number is the number of dots in an equilateral triangle uniformly filled with dots. For example, three dots can be arranged in a triangle; thus three is a triangle number. The nth triangle number is the number of dots in a triangle with n dots on a side.
A triangle number is, equivalently, the sum of the nnatural numbers from 1 to n.
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