作者chengyuyang ()
看板GMAT
标题Re: [计量] GWD-PS几题
时间Wed Nov 21 23:59:24 2007
※ 引述《mimiwei955 (霖)》之铭言：
: 1.
: Three printing presses, R, S, and T, working together at their respective
: constant rates, can do a certain printing job in 4 hours. S and T,
: working together at their respective constant rates, can do the same job
: in 5 hours.
: How many hours would it take R, working alone at its constant rate,
: to do the same job?
: A. 8
: B. 10
: C. 12
: D. 15
: E. 20
题目说的都是同一个工作 所以可以得到以下式子
(1)1/R+1/S+1/T=1/4
(2)1/S+1/T=1/5
(1)-(2)= 1/R=1/4-1/5 R=20
: 2.
: This year Henry will save a certain amount of his income, and he will spend t
: he rest. Next year Henry will have no income, but for each dollar that
: he saves this year, he will have 1 + r dollars available to spend.
: In terms of r, what fraction of his income should Henry save this year so that
: next year the amount he was available to spend will be equal to half
: the amount that he spends this year?
: A. 1/(r+2)
: B. 1/(2r+2)
: C. 1/(3r+2)
: D. 1/(r+3)
: E. 1/(2r+3)
: 两题答案都是E
: 麻烦大家帮我解答
: 万分感谢！！！
依题意之道income的用途只有save 和spend
设I=Sa+Sp
问今年要存占income多少比例的钱 明年才可以花1/2今年花的钱
Sa(1+r)=1/2Sp
2Sa(1+r)=Sp
两边相加Sa
2Sa(1+r)+Sa=Sp+Sa
Sa(2+2r+1)=I
Sa/I=1/(2r+3)
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※ 编辑: chengyuyang 来自: 219.81.167.234 (11/22 00:15)
1F：推 mimiwei955:非常感谢～原来1+r是比例的含意....难怪我作不出来～哈 11/22 11:25
2F：推 chengyuyang:1+r在这里应该是利息的观念唷 11/22 11:37
3F：→ chengyuyang:今年存sa的钱 依题意 明年变成sa(1+r) 11/22 11:37
4F：推 mimiwei955:原来如此～谢谢C大^^ 11/22 14:13