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pt question

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by jamesk486 » Sun May 06, 2007 8:20 am
The price of a dress was first discounted by a certain percent and later by 25 percent of the discounted price. If these two discounts are equivalent to a single discount of 40% of the original price, what was the first discount?
A. 10%
B. 15%
C. 20%
D. 30%
E. 65%

The rear wheels of a car crossed a certain line 0.5 second after the front wheels crossed the same line. If the centers of the front and rear wheels are 20 feet apart and the car traveled in a straight line at a constant speed, which of the following gives the speed of the car in miles per hour?

A. (20/5.280)(60^2/0.5)
B. (20/5.280)(60/0.5)
C.(20/5.280)(0.5/60^2)
D. (20)(5.280) / (60^2)(0.5)
E. (20)(5.280) / (60)(0.5)
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Source: — Problem Solving |

Re: pt question

by jayhawk2001 » Sun May 06, 2007 10:21 am
jamesk486 wrote:The price of a dress was first discounted by a certain percent and later by 25 percent of the discounted price. If these two discounts are equivalent to a single discount of 40% of the original price, what was the first discount?
A. 10%
B. 15%
C. 20%
D. 30%
E. 65%
Let x be the first discount.

(1-x)(.75) = 0.6

Solving for x, we get 0.2 i.e. 20%

jamesk486 wrote: The rear wheels of a car crossed a certain line 0.5 second after the front wheels crossed the same line. If the centers of the front and rear wheels are 20 feet apart and the car traveled in a straight line at a constant speed, which of the following gives the speed of the car in miles per hour?

A. (20/5.280)(60^2/0.5)
B. (20/5.280)(60/0.5)
C.(20/5.280)(0.5/60^2)
D. (20)(5.280) / (60^2)(0.5)
E. (20)(5.280) / (60)(0.5)
I guess we need the conversion factor between feet and miles to
answer this.

0.5 * speed = 20 feet
0.5 / (60*60) * speed = 20 feet (convert sec to hour)

speed = (20 * 60 * 60 / 0.5) feet/hr
speed = (20 * 60 * 60) / (0.5 * 5280) miles/hr

I'm not too sure if GMAT expects you to remember conversion
factors from feet to miles.
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by Cybermusings » Sun May 06, 2007 11:44 am
The rear wheels of a car crossed a certain line 0.5 second after the front wheels crossed the same line. If the centers of the front and rear wheels are 20 feet apart and the car traveled in a straight line at a constant speed, which of the following gives the speed of the car in miles per hour?

A. (20/5.280)(60^2/0.5)
B. (20/5.280)(60/0.5)
C.(20/5.280)(0.5/60^2)
D. (20)(5.280) / (60^2)(0.5)
E. (20)(5.280) / (60)(0.5)

20 feet is the distance which is covered in .5 seconds...

20 ft = 20/5280 miles
.5 sec = .5/60*60 hrs
Speed = Distance/Time
= (20/5280) / [.5/3600]
= (20/5280)*3600/.5

So option A
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Re: pt question

by mmslf75 » Sun Aug 16, 2009 1:32 am
jamesk486 wrote:The price of a dress was first discounted by a certain percent and later by 25 percent of the discounted price. If these two discounts are equivalent to a single discount of 40% of the original price, what was the first discount?
A. 10%
B. 15%
C. 20%
D. 30%
E. 65%

I have yet another method to this...
When you have two such percentages acting one after the other..

a + b + (ab/100) = Effective Percentage

a - 25 + a (-25/100) = -40
a - 25 - (a/4) = -40
3a = - 160 + 100
a = -20 => Discount of 20 percent
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