BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

★★★★★5.0559 reviews
GMATBootcamp Starts Sep 28
Chris Peckover, Target Test Prep GMAT expert
LIVE ONLINE BOOTCAMP

Live Online Bootcamp Class with Top GMAT Expert Chris Peckover

15 live classes from Sep 28, 2026

Schedule
Mon to Fri · 7:00 to 10:00 PM ET
Included
Live classes + 6 months of TTP OnDemand
  • Boost your GMAT score in less than one month in a live online class
  • 6 months access to TTP OnDemand video courses included
View bootcamp & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

Algebra - Ages of Al and Bob

Expert replies
Post new topic Post Reply
Previous Topic Next Topic

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770
by Brent@GMATPrepNow » Wed Jan 28, 2009 8:59 am
In three years, Bob will be three-fourths as old as Al. In 11 years, Bob will be five-sixths as old as Al. What is the sum of their current ages?
(A) 15
(B) 19
(C) 22
(D) 24
(E) 28
Please note that this is not an official GMAT question; it’s my attempt to create difficult (650+ level) GMAT-style questions for this forum.
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
Community Manager
Posts: 1049
Joined: Sun Apr 06, 2008 5:15 pmFollowed by: 27 members
Location: Pittsburgh, PA
Thanked: 113 times
GMAT Score:710

by dmateer25 » Wed Jan 28, 2009 9:12 am
A = al
B = Bob

3/4(a+3) = b +3
3a + 9 = 4b + 12
3a = 4b + 3
a = 4b+3/3


5/6(a+11)=b+11
5a + 55 = 6b + 66
5a = 6b + 11
a = (6b + 11)/5
(4b+3)/3 = (6b + 11)/5
20b + 15 = 18b + 33
2b = 18
b=9

substituting b back in

a = (4(9)+3)/3
a= 39/3
a = 13

13 + 9 = 22

I will go with C
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Wed Jan 28, 2009 9:22 am
Nice work, dmateer25. The answer is C.
I'm posting my solution as well, because it is slightly different.

Image
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 44
Joined: Thu Nov 20, 2008 2:18 pm
Thanked: 1 times

by mdavis » Wed Jan 28, 2009 11:58 am
Thanks for the explanation to this problem. I had a question regarding the explained answer though.

Why do you at the very end multiply Bob's age by 5/6 on only one side of the equation? I always thought that you have to do things to both sides?

Thanks!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Wed Jan 28, 2009 12:32 pm
mdavis wrote:Thanks for the explanation to this problem. I had a question regarding the explained answer though.

Why do you at the very end multiply Bob's age by 5/6 on only one side of the equation? I always thought that you have to do things to both sides?

Thanks!
You're right that we must always perform the same operations to both sides of an equation. However, up until the point where we multiplied Al's age by 5/6, we didn't have an equation. We multiplied by 5/6 to create an equation.

For example, let's say that I'm twice as old as you. For the moment, we can't say that our two ages are equal (which means that we can't create an equation).
However, we could say that our ages are equal if we fiddled with one of our ages.
For example, if we doubled your age, then our ages would be equal. The equation would be: (my age) = 2(your age)

Another way to make our ages equal would be to halve my age. That would make us the same age. In this case, the equation would be: 1/2(my age) = (your age)

I hope that helps.
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1