GMAT OFFICIAL GUIDE DS

Solution:

We are given that Sara’s age is twice Bill’s age. If we let Sara’s current age = S and Bill’s current age = B, we can create the following equation:

S = 2B

We need to determine Sara’s current age.

Statement One Alone:

Four years ago, Sara’s age was exactly 3 times Bill’s age.

Using the information in statement one we can create the following equation, noting that we must subtract 4 from both Sara’s current age and Bill’s current age to determine their respective ages 4 years ago:

S – 4 = 3(B – 4)

Since we have the equation S = 2B, from the given information we see that we have enough information to determine Sara’s age. Let’s complete the problem, even though it is not necessary.

2B – 4 = 3(B – 4)

2B – 4 = 3B – 12

B = 8 and thus S = 2B = 16

Statement one alone is sufficient to answer the question. We can eliminate answer choices B, C, and E.

Statement Two Alone:

Eight years from now, Sara’s age will be exactly 1.5 times Bill’s age.

Using the information in statement two we can create the following equation, noting that we must add 8 to both Sara’s current age and Bill’s current age to determine their respective ages in 8 years:

S + 8 = 1.5(B + 8)

Since we have the equation S = 2B, from the given information we see that we have enough information to determine Sara’s age. Statement two alone is sufficient to answer the question.

Answer: D

About The Author

Jeffrey Miller is the head GMAT instructor for Target Test Prep. Jeff has more than fourteen years of experience in the business of helping students with low GMAT scores hurdle the seemingly impossible and achieve the scores they need to get into the top 20 business school programs in the world, including HBS, Stanford, Wharton, and Columbia. Jeff has cultivated many successful business school graduates through his GMAT instruction, and will be a pivotal resource for many more to follow.