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一道2005 9月51题

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楼主
发表于 2006-8-7 22:10:00 | 只看该作者

一道2005 9月51题

51.

The toll for crossing a certain bridge is $0.75 each crossing. Drivers who frequently use the bridge may instead purchase a sticker each month for $13.00 and then pay only $0.30 each crossing during that month. If a particular driver will cross the bridge twice on each of x days next month and will not cross the bridge on any other day, what is the least value of x for which this driver can save money by using the sticker?

A. 14

B. 15

C. 16

D. 28

E. 29

SA:B 怎样做的啊..........

http://forum.chasedream.com/dispbbs.asp?boardID=22&ID=131409&page=1
沙发
发表于 2006-8-7 22:51:00 | 只看该作者

x*2*0.75 > 13+x*2*0.3

x > 13/0.9=14.4

x = 15


[此贴子已经被作者于2006-8-8 17:10:42编辑过]
板凳
发表于 2006-8-8 16:28:00 | 只看该作者

题目中不是说  driver will cross the bridge twice on each of x days? 

是否应该是 x*2*0.75〉13+x*2*0.3?

地板
发表于 2006-8-8 17:09:00 | 只看该作者
答案是B吧。
5#
发表于 2006-8-8 17:10:00 | 只看该作者
以下是引用CrystalLion在2006-8-8 16:28:00的发言:

题目中不是说  driver will cross the bridge twice on each of x days? 

是否应该是 x*2*0.75〉13+x*2*0.3?

对!

已经改过来了

谢谢CrystalLion!!

6#
发表于 2006-8-8 17:15:00 | 只看该作者
以下是引用CrystalLion在2006-8-8 16:28:00的发言:

题目中不是说  driver will cross the bridge twice on each of x days? 

是否应该是 x*2*0.75〉13+x*2*0.3?

correct!

7#
发表于 2006-8-8 17:19:00 | 只看该作者

这下被大家鄙视了~~

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