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cracksat
 Post subject: Percentage change in price
PostPosted: Sun Oct 07, 2007 10:02 pm 
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Posts: 19
If the price of a mobile phone decreased by 25% to $90, then what was the original price of the mobile phone?

A. $22.5
B. $112.5
C. $120
D. $30
E. $115
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alex
 Post subject:
PostPosted: Mon Oct 08, 2007 6:38 am 
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The answer is $120.
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dave
 Post subject: Percentage change of old price or new price?
PostPosted: Fri Oct 12, 2007 6:45 pm 
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Isn't 25% of 90 22.5

Then the price before the reduction should be 112.5.

What is the OA anyway?
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cracksat
 Post subject: % change is always a percent of the initial value
PostPosted: Sun Oct 14, 2007 4:25 pm 
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Joined: Tue May 22, 2007 1:28 pm
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The OA is 120.

% change is always a percentage of the initial value.

When we say that the price decreased by 25%, we always measure it as a % of what the price was before the decrease.

In this case the way to proceed is

Let the initial price be 'p'. Then if the price decreased by 25%, the decrease of 25% is on 'p'.

So, the new price will be p - 25% of p = 75% of p
And the question says that the new price is 90.

So, 75% of 'p' = 90

i.e., 75p/100 = 90

or p = 90*100 / 75 = 120.
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