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Computer price

by SaraLotfy » Wed Oct 09, 2013 8:20 am
The average computer price today is $700. If the average computer price 3 years ago was 80% of the price today, what was the percentage increase in the average computer price over the past 3 years?

A)15%
B)20%
C)25%
D)50%
E)80%
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by Brent@GMATPrepNow » Wed Oct 09, 2013 8:39 am
SaraLotfy wrote:The average computer price today is $700. If the average computer price 3 years ago was 80% of the price today, what was the percentage increase in the average computer price over the past 3 years?

A)15%
B)20%
C)25%
D)50%
E)80%
Since the question asks us to find the PERCENT increase, the $700 information is unnecessary.
Let's pick a nice value for the current average price.
Let's say the the current average price is $100
This means that the average price 3 years ago was $80

So, what is the PERCENT increase from $80 to $100?
Percent increase = 100(change in value)/(original value)
= 100(100 - 80)/80
= [spoiler]25%[/spoiler]
= C

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by theCodeToGMAT » Wed Oct 09, 2013 9:15 am
Today's Price = 700$

Average Price 3 years ago = 80*700/100 = 4 * 140 = 560

Percentage Increase = 700-560/560 = 140/560 = 1/4 = 25%

Answer [spoiler]{C}[/spoiler]
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by GMATGuruNY » Wed Oct 09, 2013 11:20 am
SaraLotfy wrote:The average computer price today is $700. If the average computer price 3 years ago was 80% of the price today, what was the percentage increase in the average computer price over the past 3 years?

A)15%
B)20%
C)25%
D)50%
E)80%
If X is 2/3 of Y, then Y is 3/2 of X.
If X is 4/5 of Y, then Y is 5/4 of X.

The price 3 years ago = 80/100 = 4/5 of today's price.
Thus:
Today's price = 5/4 of the price 3 years ago -- an increase of 1/4 = 25%.

The correct answer is C.
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