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crossing a bridge...

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crossing a bridge...

by LevelOne » Sun Jun 21, 2009 6:50 am
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

thanks!
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by mikeCoolBoy » Sun Jun 21, 2009 8:34 am
The stimulus says that the driver will pass twice per day, so without the plan the cost will be (0.75 + 0.75)x and with the plan 13 + (0.3 + 0.3)x.

The question asks you to find the value of x for which the driver will save money by using the plan

13 + 0.6x < 1.5x ---> 13 < 0.9x --->x > 13/0.9 ---> x > 14.444

so x=15 making B the correct answer.
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by LevelOne » Sun Jun 21, 2009 9:23 am
great, your explanation seems to be easier than the official one :lol:
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