From a bag containing 12 identical blue balls, y identical yellow balls, and no other balls, one ball will be removed at random.If the probability is less than 2/5 that the removed ball will be blue, what is the least number of yellow balls that must be in the bag?
(A) 17
(B) 18
(C) 19
(D) 20
(E) 21
题目是明白了~但是做错了我列的等式是12/12+y=2/5，但是算出来是18阿··
根据题意应当是不等式12/(12+y)<2/5，而非=式。化简过后：12/(12+y)<12/30 =>12+y>30=>y>18
Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?
(A) 1/2
(B) 1/3
(C) 1/4
(D) 1/5
(E) 1/6
大家能说一说这题吗？俺也是弄不懂阿···
设存x刀/月，不存的y刀/月。一年下来存12x刀。一年存的12x刀是3倍鱼一月不存的y刀=>12x=3y=>y=4x。
问题问的是每月存的钱是每月收入的百分比，即x/(x+y),将y=4x带入后得出1/5
Are at least 10 percent of the people in Country X who are 65 yearsold or older employed?
(1)In Country X,11.3 percent of the population is 65 years old or older;;% r! z1 B* (2）In Country X,of the population 65years old or older,20percent of the men and 10 perccent of the women are employed.& m/ k% H: M- B) U9 f
答案：B6 M8 Q; h% w* P; X
第一个条件只说了有11.3%的人大于等于65岁
第二个条件只说了大于等于65岁的人里面有20%的男性和10%的女性是有工作的
但是问题问的是percent of the people in Country X，而不是percent of the population 65years old or older，为什么是b呢？
题目问的是X城里那些年纪>=65岁的受雇的人数与X城中年纪>=65岁的人数比例>=10%？
2）大于等于65岁的人中20%的男性受雇，10%的女性受雇。=>30%。所以已经超过10%。
A thin piece of wire 40 meters long is cut into two pieces.One piece is used to form a circle with radius r, and the other is used to form a square.No wire is left over.Which of the following represents the total area, in square meters, of the circular and the square regions in terms of r ?
(A) πr2
(B)πr2 + 10
(C)πr2+ 1/4π2r2
(D)πr2 + (40 - 2πr)2
(E)πr2 + (10 – 1/2πr)2
我选的是d，请问为什么是e的？
由圆的半径为r推出周长是2πr.所以这个wire第一段的长是2πr。那么剩下的那段就是40-2πr.可以推出正方形的变长为（40-2πr）/4=>10-1/2πr
-- by 会员 小娟子nana (2010/4/9 20:03:05)
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发表于 2010-4-9 20:03:05
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