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

BTGModeratorVI wrote: ↑

Sun Jul 19, 2020 1:49 pm

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.

Answer: B
Source: GMAT paper tests

Let's take each statement one by one.

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

Since we do not know the value of the antique on 31 December 1981, we can't find the percent increase in the value of the antique. Insufficient.

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

Say the value of the antique on 1 Jan'81 was $x; thus, its value of 31 Dec'81 was $2x. Thus, the percentage increase in value = [(2x – x)/x]*100% = 100%

Correct answer: B

Hope this helps!

-Jay
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BTGModeratorVI wrote: ↑

Sun Jul 19, 2020 1:49 pm

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.

Answer: B
Source: GMAT paper tests

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