varun289 wrote:Each of a, b, and c is positive. Does B = root AC ?

STATEMENT 1: a/b = b/c
STATEMENT 2: 1/b^3 = 1/(ABC)

Target question: Does B = sqrt(AC)?

This is a great candidate for rephrasing the target question.
Take B = sqrt(AC) and square both sides to get: B^2 = AC

Rephrased target question: Does B^2 = AC?

Aside: If anyone is interested, we have a free video on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100

Statement 1: A/B = B/C
Cross multiply to get B^2 = AC
Perfect. This means that B^2 definitely equals AC
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: 1/B^3 = 1/(ABC)
Cross multiply to get B^3 = ABC
Divide both sides by B to get B^2 = AC
Perfect. This means that B^2 definitely equals AC
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = D

NOTE: Our solution was made easier by the fact that A, B and C are positive. For example, if it were possible that B=0, then we wouldn't be able to divide both sides of the equation by B, as we did with statement 2.

Cheers,
Brent