In ten years, David will be four times as old as Aaron.

Expert replies

VJesus12: Legendary Member; Posts: 2276; Joined: Sat Oct 14, 2017 6:10 amFollowed by: 3 members

by VJesus12 » Sat Feb 10, 2018 1:51 am

In ten years, David will be four times as old as Aaron. Twenty years ago, David was twice as old as Ellen. If David is seven years older than Ellen, how old is Aaron?

A. 1-5
B. 6-10
C. 11-15
D. 16-20
E- 21-25

The OA is the option A.

I've got confused here. How should I set the equations to solve this PS question? Experts, I'd be thankful for your help here. <i class="em em-grinning"></i>

Like this post

Source: Beat The GMAT — Problem Solving | Sat Feb 10, 2018 1:51 am

regor60: Master | Next Rank: 500 Posts; Posts: 416; Joined: Thu Oct 15, 2009 11:52 am; Thanked: 27 times

In ten years, David will be four times as old as Aaron.

by regor60 » Sat Feb 10, 2018 8:28 am

VJesus12 wrote:In ten years, David will be four times as old as Aaron. Twenty years ago, David was twice as old as Ellen. If David is seven years older than Ellen, how old is Aaron?

A. 1-5
B. 6-10
C. 11-15
D. 16-20
E- 21-25

The OA is the option A.

I've got confused here. How should I set the equations to solve this PS question? Experts, I'd be thankful for your help here. <i class="em em-grinning"></i>

Let T= "Now". So T+10 will be ten years from now and T-20 is 20 years ago,.

Let A, D and E be their respective ages now.

Translate the first part as follows:
D+10 = 4(A+10).
Similarly, the second prompt translates as follows: D-20 = 2(E-20)
And the third part: D = E+7

Let's save the first equation, D+10=4(A+10) and try to find D so that we can solve for A.

Let's solve for E using the third equation,
E=D-7
Substitute this into the second equation:
D-20=2((D-7)-20). Solving for D = 34.

Plug D=34 into the first equation:
34+10=4(A+10)

4A=4 > A= 1, A

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Sat Feb 10, 2018 10:54 am

Hi VJesus12,

We're told that in TEN years, David will be FOUR times as old as Aaron. TWENTY years ago, David was TWICE as old as Ellen. David is SEVEN years older than Ellen. We're asked how old Aaron is NOW. While this question can be solved Algebraically, it can also be solved by 'playing around' with the information and a bit of 'brute force' math.

Let's start with David - since he's referenced repeatedly. We know that he was alive 20 years ago AND at that time he was TWICE as old as Ellen. Thus, David is clearly older than 20. Let's see what happens if David is currently 30....

IF.... right now, David = 30, then....
20 years ago, David = 10 and Ellen = 5
However, this does NOT match with the fact that David is supposed to be SEVEN years older than Ellen, so we have to 'work back' and adjust the numbers to account for the 7 year difference in their ages...

IF.... 20 years ago, David = 14 and Ellen = 7, then David is TWICE Ellen's age AND seven years older than Ellen.
That would make David = 34 right now.

We're told that in 10 years, David will be FOUR times as old as Aaron...
In 10 years, David = 44 and Aaron = 11....
Thus, Aaron's age right NOW = 1

Final Answer: A

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review