数学蓝皮书上碰到3道居然卡住了··· 请NN 帮帮忙吧··

xyqirene · 发表于 2010-11-4 17:50:24

137 if an organization were to sell N tickets for a theater production, the total revenue from ticket sales would be 20% greater than the total costs of the production, if the organization sold all but 5% of the N tickets, the total revenue from the ticket sales was what percent greater than the total costs of the production?

14%

我想的就是比例问题··· 两个一比··

How many liters of pure alcohol must be added to a 100-liter solution that is 20% alcohol in order to produce a solution that is 25% alcohol?

20/3

我这道题也是直接在比···

each month for 6 months the amount of money in a benefit fund is doubled, at the end of the 6 months there is a total $640 in the fund, how much money was in the fund at the end of 3 months?

80

这道题是等比数列问题不··但是怎么都算不出来··

chris2928 · 发表于 2010-11-4 18:43:56

第1个：
设单位票价为a 设成本为C（注不论销售多少C不变）
Na=(1+20%)*C
现销售95%N的票，则销售额为95%N*a
95%N*a/c-1=1.14-1=0.14
就是题目所求

第2个：
抓住加纯酒精前后，溶质不变
设加入纯酒精量为a
20%*100+a=25%*(100+a)

第3个：
640直接开根号好了
原理就像病毒。本来1个，1分钟2个，2分钟4个，3分钟8个，这样……

xyqirene · 发表于 2010-11-4 20:04:54

谢谢咯··
第一道all but 直接看飞··
下次一定小心了！！

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