Data Sufficiency

Vincen wrote:By how many years is Jason older than Allison?

(1) Jason is 6 years older than twice David's age.

(2) In 8 years, Allison will be twice as old as David is now.

[spoiler]OA=C[/spoiler]

Source: Veritas Prep

Say Jason is J years, Allison is A years, and David is D years old.

We have to find out the value of J - D.

Let's take each statement one by one.

(1) Jason is 6 years older than twice David's age.

J = 2D + 6. No information about Allison. Insufficient.

(2) In 8 years, Allison will be twice as old as David is now.

A + 8 = 2D. No information about Jason. Insufficient.

(1) and (2) together

From (1), we get 2D = J - 6 and from (2), we have A = 8 = 2D. Thus, J - 6 = A + 8 => J - A = 14. Sufficient.

The correct answer: C

Hope this helps!

-Jay
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Vincen wrote:By how many years is Jason older than Allison?

(1) Jason is 6 years older than twice David's age.

(2) In 8 years, Allison will be twice as old as David is now.

[spoiler]OA=C[/spoiler]

Source: Veritas Prep

Target question: By how many years is Jason older than Allison?

Statement 1: Jason is 6 years older than twice David's age.
Since we have no information about Allison, there was no way we can answer the target question.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: In 8 years, Allison will be twice as old as David is now.
Since we have no information about Jason, there was no way we can answer the target question.
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Let J = Jason's PRESENT age
Let D = David's PRESENT age
Let A = Allison's PRESENT age

From statement 1, we can write: J = 2D + 6
From statement 2, we can write: A + 8 = 2D

Take the top equation and replace 2D with A + 8 to get: J = (A + 8 ) + 6
Simplify: J = A + 14
This tells us that J is 14 greater than A
In other words, Jason is 14 years older than Allison

Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent