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

It is currently 22 Oct 2018, 08:07

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

If X = 0.(81), where the brackets around the 2-digit sequence 81 indic

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

Hide Tags

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 50039
If X = 0.(81), where the brackets around the 2-digit sequence 81 indic  [#permalink]

Show Tags

New post 28 Mar 2018, 03:10
1
6
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

58% (01:08) correct 42% (01:49) wrong based on 65 sessions

HideShow timer Statistics

If X = 0.(81), where the brackets around the 2-digit sequence 81 indicates the sequence repeats indefinitely, what is the value of 99*X?

(A) 80.(19)
(B) 80.19
(C) 81
(D) 81.81
(E) 81.(81)

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

examPAL Representative
User avatar
G
Joined: 07 Dec 2017
Posts: 724
Re: If X = 0.(81), where the brackets around the 2-digit sequence 81 indic  [#permalink]

Show Tags

New post 28 Mar 2018, 03:29
1
Bunuel wrote:
If X = 0.(81), where the brackets around the 2-digit sequence 81 indicates the sequence repeats indefinitely, what is the value of 99*X?

(A) 80.(19)
(B) 80.19
(C) 81
(D) 81.81
(E) 81.(81)


We'll break our complex calculation (x99) into small, easy bits (x100 - x1)
This is a Precise approach.

100*X would be 81.818181818181 with infinite 81 after the decimal point.
That is, 100*X = 81.(81)
So 99*X 100*X - X = 81.(81) - 0.(81) = 81

(C) is our answer.
_________________

Image
Sign up for 7-day free trial
Image

I am a CR Expert - Ask Me ANYTHING about CR
I am a DS Expert - Ask Me ANYTHING about DS


Watch free GMAT tutorials in Math, Verbal, IR, and AWA.

GMAT test takers: Watch now the GMAC interview with the people who write the GMAT test!
We discussed the chances of improving a GMAT score; how important the first questions on the test are; what to do if you don’t have enough time to complete a whole section; and more.

You can watch all the action from the interview here.

Senior SC Moderator
avatar
V
Joined: 22 May 2016
Posts: 2040
Premium Member CAT Tests
If X = 0.(81), where the brackets around the 2-digit sequence 81 indic  [#permalink]

Show Tags

New post 31 Mar 2018, 00:33
Bunuel wrote:
If X = 0.(81), where the brackets around the 2-digit sequence 81 indicates the sequence repeats indefinitely, what is the value of 99*X?

(A) 80.(19)
(B) 80.19
(C) 81
(D) 81.81
(E) 81.(81)

One way to approach these questions is to set up a simple subtraction in which the repeating part is positioned to be subtracted from itself.

A repeating decimal is some fraction, x
Let x = .818181...
(Start with the repeating portion.)

Essentially, multiply the repeating decimal by some power of 10 so that you can subtract the repeating portion away.

This decimal repeats every two numbers.
Use 100*x to move the decimal two places to the right.
Thus 100x = 81.81818181....

Subtract x from 100x, and
Subtract 0.8181... from 81.8181...

100x = 81.818181...
___-x =_-0.818181...
__99x = 81

Answer C

(The fraction, x, would be \(\frac{81}{99}=\frac{9}{11}\))

For related topic and slightly different method see Bunuel how to convert a recurring decimal to fraction.

The method I used (multiply by a power of 10) is explained HERE.
_________________

___________________________________________________________________
For what are we born if not to aid one another?
-- Ernest Hemingway

Manager
Manager
avatar
B
Joined: 16 May 2017
Posts: 52
Location: India
WE: General Management (Retail Banking)
CAT Tests
Re: If X = 0.(81), where the brackets around the 2-digit sequence 81 indic  [#permalink]

Show Tags

New post 31 Mar 2018, 01:31
Bunuel wrote:
If X = 0.(81), where the brackets around the 2-digit sequence 81 indicates the sequence repeats indefinitely, what is the value of 99*X?

(A) 80.(19)
(B) 80.19
(C) 81
(D) 81.81
(E) 81.(81)
X=.(81); 100X=81.(81); 100X=81+.(81);100X=81+X;X=81/99
Answer C

Sent from my Redmi 4 using GMAT Club Forum mobile app
_________________

"The harder you work the luckier you get"

Intern
Intern
avatar
B
Joined: 15 Apr 2017
Posts: 43
Re: If X = 0.(81), where the brackets around the 2-digit sequence 81 indic  [#permalink]

Show Tags

New post 04 Apr 2018, 17:43
This is the weirdest question ever considering that the question asks about .81 repeating and the answer is in whole format. I mean the real answer is 80.999 repeating.

I think this question is incorrectly worded
GMAT Club Bot
Re: If X = 0.(81), where the brackets around the 2-digit sequence 81 indic &nbs [#permalink] 04 Apr 2018, 17:43
Display posts from previous: Sort by

If X = 0.(81), where the brackets around the 2-digit sequence 81 indic

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


cron
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®.