Target Test Prep 20% Off Flash Sale is on! Code: FLASH20

Redeem
Target Test Prep Flash Sale
Target Test Prep is 20% off right now!
Use code FLASH20

Available with Beat the GMAT members only code

MORE DETAILS
Target Test Prep Flash Sale
Magoosh
Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

MORE DETAILS
Magoosh

Algebra

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Junior | Next Rank: 30 Posts
Posts: 26
Joined: Tue Feb 02, 2016 10:25 am
Thanked: 1 times

Algebra

by John fran kennedi » Wed Mar 09, 2016 10:25 am
Image


Hello guys, I have just practiced the GMAT, as we can see on this image , I get confused to solve this. I have seen the answer explanation , but I don't understand well. I don't know whether because I don't get the question well or not.
In the answer explanation ( OG 2016) page 245, it states
=10,000(0.0012)-100(0.0012)
=12,12 - 0,12

I don't know why it's 12,12, not 12.

I do need your help to make me understand. Thanks in advance
Top

GMAT/MBA Expert

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

by Brent@GMATPrepNow » Wed Mar 09, 2016 10:34 am
A bar over a sequence of digits in a decimal indicates that the sequence repeats indefinitely. What is the value of (10^4 - 10^2) (0.0012)?

Note: There is a bar over "12" in 0.0012.

(A) 0
(B) 0.12 (with the bar over the 12)
(C) 1.2
(D) 10
(E) 12
(10� - 10²)(0.00121212...) = 10�(0.00121212...) - 10²(0.00121212...)
= 12.121212... - 0.121212...
= 12 (since the decimal parts, in blue, are identical, they cancel out]

Answer: E

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top

GMAT/MBA Expert

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

by Brent@GMATPrepNow » Wed Mar 09, 2016 10:35 am
A bar over a sequence of digits in a decimal indicates that the sequence repeats indefinitely. What is the value of (10^4 - 10^2) (0.0012)?

Note: There is a bar over "12" in 0.0012.

(A) 0
(B) 0.12 (with the bar over the 12)
(C) 1.2
(D) 10
(E) 12
We can also apply some number sense here.

(10� - 10²)(0.00121212...) = (10,000 - 100)(0.00121212...)
= 9900(0.00121212...)
= (a bit less than 10,000)(0.00121212...)

Well, (10,000)(0.00121212...) = 12.121212
So, (a bit less than 10,000)(0.00121212...) = a bit less than 12.121212...

Check the answer choices:
A) 0
B) 0.121212...
C) 1.2
D) 10
E) 12

E is the best match

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
User avatar
Junior | Next Rank: 30 Posts
Posts: 26
Joined: Tue Feb 02, 2016 10:25 am
Thanked: 1 times

by John fran kennedi » Wed Mar 09, 2016 10:47 am
Wow, I really do understand now. Thank you so much
Top
GMAT Instructor
Posts: 2630
Joined: Wed Sep 12, 2012 3:32 pm
Location: East Bay all the way
Thanked: 625 times
Followed by:119 members
GMAT Score:780

by Matt@VeritasPrep » Thu Mar 17, 2016 9:26 pm
Another idea here: since (xy/99) = .xyxyxyxy..., we can say that

.0012121212... =

.12121212... * (1/100) =

12/99 * 1/100 =

12/9900

Now we have

(10� - 10²) * 12/9900 =

9900 * 12/9900 =

12

and we're set!
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Mon Oct 09, 2017 7:33 am
A common mistake that students make on a problem like this is to subtract the exponents. But of course we cannot subtract the exponents when we're subtracting terms with the same base.

More on this here: https://www.beatthegmat.com/fdp-problem- ... tml#763953
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 7251
Joined: Sat Apr 25, 2015 10:56 am
Location: Los Angeles, CA
Thanked: 43 times
Followed by:29 members

by Scott@TargetTestPrep » Sun Nov 24, 2019 5:45 pm
A bar over a sequence of digits in a decimal indicates that the sequence repeats indefinitely. What is the value of (10^4 - 10^2) (0.0012)?

Note: There is a bar over "12" in 0.0012.

(A) 0
(B) 0.12 (with the bar over the 12)
(C) 1.2
(D) 10
(E) 12
Remember that the notation [12] means there is a bar over the 12, indicating that the decimal is non-terminating.

Now, let's start the problem by factoring out 10^2 from (10^4 - 10^2). This gives us:

(10^4 - 10^2) (0.00[12])

10^2 (10^2 - 1)(0.00[12])

We can distribute 0.00[12] with the two quantities in the parentheses. This gives us:

10^2(0.[12] - 0.00[12])

100(0.[12] - 0.00[12])

12.[12] - 0.[12] = 12

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage
Top
Post new topic Post Reply
• Page 1 of 1