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What was the percent increase in the value of a certain

by VJesus12 » Wed Apr 18, 2018 1:39 am

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What was the percent increase in the value of a certain antique from January 1, 1981, to December 31, 1981?

(1) The value of the antique on January 1, 1981, was $3,000.
(2) The value of the antique on December 31, 1981, was double the value of the antique on January 1,1981.

The OA is B.

How can I get an answer just with the second statement? Are not necessary both statements? I'd appreciate any help.
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by GMATGuruNY » Wed Apr 18, 2018 3:59 am

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VJesus12 wrote:How can I get an answer just with the second statement?
If a value DOUBLES, then it increases by 100%:
x + (100% of x) = x + x = 2x.
Thus, Statement 2 indicates that the percent increase = 100.
SUFFICIENT.
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by Brent@GMATPrepNow » Wed Apr 18, 2018 5:27 am

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VJesus12 wrote:What was the percent increase in the value of a certain antique from January 1, 1981, to December 31, 1981?

(1) The value of the antique on January 1, 1981, was $3,000.
(2) The value of the antique on December 31, 1981, was double the value of the antique on January 1, 1981.
Target question: What was the percent increase in the value of a certain antique from January 1, 1981, to December 31, 1981?

Percent increase = 100(new - old)/old
So, we can answer the target question if we have the OLD value and the NEW value.

Statement 1: The value of the antique on January 1, 1981, was $3,000.
Okay, so we have the OLD value, but we don't know the NEW value.
So, we don't have enough info to answer the target question
Statement 1 is NOT SUFFICIENT

Statement 2: The value of the antique on December 31, 1981, was double the value of the antique on January 1, 1981.
Although we aren't given specific numbers for the OLD value and NEW value, we still have enough information. Here's why:
Let x = the value of December 31, 1981
This means 2x = the value on January 1, 1981

When we apply the above formula, we get: percent increase = 100(2x - x)/x = 100x/x = 100
So, the answer to the target question is 100 percent
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer: B

Cheers,
Brent
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by Jeff@TargetTestPrep » Mon Apr 23, 2018 4:02 pm

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VJesus12 wrote:What was the percent increase in the value of a certain antique from January 1, 1981, to December 31, 1981?

(1) The value of the antique on January 1, 1981, was $3,000.
(2) The value of the antique on December 31, 1981, was double the value of the antique on January 1,1981.
We need to determine the percent increase in the value of a certain antique from January 1, 1981, to December 31, 1981.

Statement One Alone:

The value of the antique on January 1, 1981, was $3,000.

We are given the value of the antique on January 1, 1981, however, since we don't know the value of the antique on December 31, 1981, we can't determine the percent increase. Statement one alone is not sufficient.

Statement Two Alone:

The value of the antique on December 31, 1981, was double the value of the antique on January 1,1981.

One might conclude that statement two is not sufficient because neither the value of the antique on January 1, 1981 nor on December 31, 1981 is given. However, when we are given that the value has been doubled, the percent increase is always 100%. If one doesn't see that, we can let the value on January 1, 1981 be v, thus the value on December 31, 1981 will be 2v. So, the percent increase is:

(2v - v)/v x 100 = v/v x 100 = 1 x 100 = 100 percent

Answer: B

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