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
GMATLiveTeach Starts Oct 17
Chris Peckover, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Chris Peckover, 100th-Percentile GMAT Scorer

Oct 17 · Chris Peckover
Sat · 11:00 AM to 2:00 PM ET
Oct 20 · Chris Peckover
Tue, Thu · 8:00 to 10:00 PM ET
Oct 25 · Josh Braslow
Sun · 1:00 to 4:00 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemand 5 seats left Start anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

165+ EA score guarantee
$05-day trial no automatic billing
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 Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget 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.

Reciprocals

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Wed May 25, 2011 9:40 am
by TuanNguyen87 » Thu Jun 09, 2011 12:21 am
In an electric circuit, two resistors with resistances x and y are connected in parallel. In this case, if r is the combined resistance of these two resistors, then the reciprocal of r is equal to the sum of the reciprocals of x and y. What is r in terms of x and y?

A. xy
B. x + y
C. 1/(x+y)
D. xy/(x+y)
E. (x+y)/xy

Answer: D

Thanks a lot in advance!!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
Legendary Member
Posts: 1448
Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members
Location: India
Thanked: 375 times

by Frankenstein » Thu Jun 09, 2011 12:23 am
Hi,
(1/r) = (1/x)+(1/y) = (x+y)/xy
So, r = xy(x+y)

Hence, D
Cheers!

Things are not what they appear to be... nor are they otherwise
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 1309
Joined: Mon Apr 04, 2011 5:34 amFollowed by: 123 members
Location: India
Thanked: 310 times
GMAT Score:750

by cans » Thu Jun 09, 2011 12:25 am
1/r = 1/x + 1/y = (x+y)/xy
thus r = xy/(x+y)
IMO D
If my post helped you- let me know by pushing the thanks button ;)

Contact me about long distance tutoring!
[email protected]

Cans!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Wed May 25, 2011 9:40 am

by TuanNguyen87 » Thu Jun 09, 2011 12:26 am
Frankenstein wrote:Hi,
(1/r) = (1/x)+(1/y) = (x+y)/xy
So, r = xy(x+y)

Hence, D
Wow you're so smart and quick :shock: But can you explain for me more about reciprocals? I have no idea about this. Thanks so much!!!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Wed May 25, 2011 9:40 am

by TuanNguyen87 » Thu Jun 09, 2011 12:27 am
You guys are really smart :shock: Thanks!!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Newbie | Next Rank: 10 Posts
Posts: 2
Joined: Wed Mar 16, 2011 4:27 pm
Location: China - Shanghai
GMAT Score:460

by kcstej » Thu Jun 09, 2011 12:29 am
1/r= 1/x + 1/y
1/r= (x+y)/xy
r= xy/(x+y)

So D
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 1448
Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members
Location: India
Thanked: 375 times

by Frankenstein » Thu Jun 09, 2011 1:00 am
TuanNguyen87 wrote:
Frankenstein wrote:Hi,
(1/r) = (1/x)+(1/y) = (x+y)/xy
So, r = xy(x+y)

Hence, D
Wow you're so smart and quick :shock: But can you explain for me more about reciprocals? I have no idea about this. Thanks so much!!!!
Hi,
If you have any specific doubt about reciprocals or whatever, you can just PM me.
Cheers!

Things are not what they appear to be... nor are they otherwise
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Thu Jun 09, 2011 2:05 am
TuanNguyen87 wrote:In an electric circuit, two resistors with resistances x and y are connected in parallel. In this case, if r is the combined resistance of these two resistors, then the reciprocal of r is equal to the sum of the reciprocals of x and y. What is r in terms of x and y?

A. xy
B. x + y
C. 1/(x+y)
D. xy/(x+y)
E. (x+y)/xy

Answer: D

Thanks a lot in advance!!!
We can plug in values for x and y.

Let x=2, y=3.
Then the reciprocals of x and y are 1/2 and 1/3.
Since the reciprocal of r is equal to the sum of the reciprocals of x and y, we get:
1/r = 1/2 + 1/3
1/r = 3/6 + 2/6
1/r = 5/6
r = 6/5. This is our target.

Now we plug x=2 and y=3 into the answers to see which yields our target of 6/5.

Only answer choice D works:
xy/(x+y) = (2*3)/(2+3) = 6/5.

The correct answer is D.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 401
Joined: Tue May 24, 2011 1:14 amFollowed by: 5 members
Thanked: 37 times

by MBA.Aspirant » Thu Jun 09, 2011 5:34 am
TuanNguyen87 wrote:In an electric circuit, two resistors with resistances x and y are connected in parallel. In this case, if r is the combined resistance of these two resistors, then the reciprocal of r is equal to the sum of the reciprocals of x and y. What is r in terms of x and y?

A. xy
B. x + y
C. 1/(x+y)
D. xy/(x+y)
E. (x+y)/xy

Answer: D


Thanks a lot in advance!!!

1/r = 1/x + 1/y

1/r = x+y/xy

r = xy / x+y
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 41
Joined: Mon Jan 10, 2011 4:54 pm
Thanked: 1 times

by Buix0065 » Fri Jul 22, 2011 1:54 pm
In this problem it states that r is the combined resistance of x and y.

So why isn't the correct answer X + Y ? Clearly I'm misunderstanding the wording of the question, just wouldn't want to miss something like this on the actual!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1