GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 13 Nov 2018, 12:51

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in November
PrevNext
SuMoTuWeThFrSa
28293031123
45678910
11121314151617
18192021222324
2526272829301
Open Detailed Calendar
  • Essential GMAT Time-Management Hacks

     November 14, 2018

     November 14, 2018

     07:00 PM PST

     08:00 PM PST

    Join the webinar and learn time-management tactics that will guarantee you answer all questions, in all sections, on time. Save your spot today! Nov. 14th at 7 PM PST
  • $450 Tuition Credit & Official CAT Packs FREE

     November 15, 2018

     November 15, 2018

     10:00 PM MST

     11:00 PM MST

    EMPOWERgmat is giving away the complete Official GMAT Exam Pack collection worth $100 with the 3 Month Pack ($299)

If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2*

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6499
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2*  [#permalink]

Show Tags

New post 13 Sep 2018, 23:42
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

78% (01:06) correct 22% (02:17) wrong based on 37 sessions

HideShow timer Statistics

[Math Revolution GMAT math practice question]

If \(\frac{1}{n(n+1)} = \frac{1}{n} – \frac{1}{(n+1)},\) then what is the value of \(\frac{1}{(1*2)} + \frac{1}{(2*3)} + \frac{1}{(3*4)} + … + \frac{1}{(99*100)}\)

\(A. \frac{1}{100}\)
\(B. \frac{1}{50}\)
\(C. \frac{49}{50}\)
\(D. \frac{99}{100}\)
\(E. \frac{1}{2}\)

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 7025
Re: If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2*  [#permalink]

Show Tags

New post 14 Sep 2018, 00:55
MathRevolution wrote:
[Math Revolution GMAT math practice question]

If \(\frac{1}{n(n+1)} = \frac{1}{n} – \frac{1}{(n+1)},\) then what is the value of \(\frac{1}{(1*2)} + \frac{1}{(2*3)} + \frac{1}{(3*4)} + … + \frac{1}{(99*100)}\)

\(A. \frac{1}{100}\)
\(B. \frac{1}{50}\)
\(C. \frac{49}{50}\)
\(D. \frac{99}{100}\)
\(E. \frac{1}{2}\)



If \(\frac{1}{n(n+1)} = \frac{1}{n} – \frac{1}{(n+1)},\) ....
So 1/(1*2)=1/1-1/2...
1/(2*3)=1/2-1/3..
So sum = 1-1/2+1/2-1/3......-1/99+1/99-1/100=1-1/100=99/100

D
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


GMAT online Tutor

CEO
CEO
User avatar
D
Joined: 11 Sep 2015
Posts: 3113
Location: Canada
Re: If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2*  [#permalink]

Show Tags

New post 14 Sep 2018, 05:54
Top Contributor
MathRevolution wrote:
[Math Revolution GMAT math practice question]

If \(\frac{1}{n(n+1)} = \frac{1}{n} – \frac{1}{(n+1)},\) then what is the value of \(\frac{1}{(1*2)} + \frac{1}{(2*3)} + \frac{1}{(3*4)} + … + \frac{1}{(99*100)}\)

\(A. \frac{1}{100}\)
\(B. \frac{1}{50}\)
\(C. \frac{49}{50}\)
\(D. \frac{99}{100}\)
\(E. \frac{1}{2}\)


If 1/n(n+1) = 1/n – 1/(n+1), then...

1/(1*2) = 1/1 - 1/2
1/(2*3) = 1/2 - 1/3
1/(3*4) = 1/3 - 1/4
.
.
.
1/(98*99) = 1/98 - 1/99
1/(99*100) = 1/99 - 1/100

So, 1/(1*2) + 1/(2*3) + 1/(3*4) + … + 1/(99*100) = (1/1 - 1/2) + (1/2 - 1/3) + (1/3 - 1/4) + . . . (1/98 - 1/99) + (1/99 - 1/100)
= 1/1 - 1/100
= 99/100

Cheers,
Brent
_________________

Brent Hanneson – GMATPrepNow.com
Image

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6499
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2*  [#permalink]

Show Tags

New post 16 Sep 2018, 17:34
=>
\(\frac{1}{(1*2)} + \frac{1}{(2*3)} + \frac{1}{(3*4)} + … + \frac{1}{(99*100)}
= (\frac{1}{1} – \frac{1}{2}) + (\frac{1}{2} – \frac{1}{3}) + (\frac{1}{3} – \frac{1}{4}) + … + (\frac{1}{99} – \frac{1}{100}) = \frac{1}{1} – \frac{1}{100} = 1 – \frac{1}{100} = \frac{99}{100}\) after cancellation of the inner terms.

Therefore, the answer is D.
Answer: D
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

GMAT Club Bot
Re: If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2* &nbs [#permalink] 16 Sep 2018, 17:34
Display posts from previous: Sort by

If 1/n(n+1) = 1/n – 1/(n+1), then what is the value of 1/(1*2) + 1/(2*

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.