作者alima (贾考柏)
看板GMAT
标题Re: [问题] GWD &PP求解
时间Tue Oct 21 01:56:55 2008
※ 引述《yyiitt1003 (小眼钢牙妹)》之铭言：
: GWD22 Q11求解 求解两道数学,请高手帮忙解答,谢谢!
: GWD22 Q11
: In a stack of cards, 9 cards are blue and the rest are red. If 2 cards are to be chosen at random from the stack without replacement,
: the probability that the cards chosen will both be blue is 6/11.What is the number of cards in the stack?
: A.10 B.11 C.12 D.15 E.18
: PP19
: The sequence a1.a2....an.. is such that an=4an-1-3 for all intergers n>1.
If a3=x, then a1=?
: A.4X-3 B.16X-15 C.(X+3)/4 D.(X+3)/16 E.(X+15)/16
题目应为 an=4a(n-1)-3
n=3, a3=x=4a2-3, (x+3)/4=a2
n=2, a2=4a1-3=(x+3)/4, a1=(x+3+12)/(4*4)
a1=(x+15)/16, E
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