It is currently 15 Dec 2017, 13:59

Decision(s) Day!:

CHAT Rooms | Olin (St. Louis) R1 | Tuck R1 | Ross R1 | Fuqua R1


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

Events & Promotions in June
Open Detailed Calendar

If (3 + a)(a/10 - 0.4) = -1, then a could be

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

Hide Tags

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42618

Kudos [?]: 135755 [0], given: 12708

If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 03 Sep 2017, 05:14
Expert's post
3
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

78% (01:13) correct 22% (01:37) wrong based on 134 sessions

HideShow timer Statistics

Kudos [?]: 135755 [0], given: 12708

Senior Manager
Senior Manager
User avatar
G
Joined: 02 Jul 2017
Posts: 281

Kudos [?]: 108 [0], given: 66

GMAT 1: 730 Q50 V38
GMAT ToolKit User CAT Tests
Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 03 Sep 2017, 05:26
given (3+a)(a/10−0.4)=−1

=>(3+a)(a−4)=−10 = (-10*1)=(-2*5)

if we try to get (-10*1) => a=7 => 10* 3 ... a=5 => 8*1

try to get (-2*5) => a=2 =>(5)*(-2) answer

Answer: D

Kudos [?]: 108 [0], given: 66

Expert Post
Top Contributor
SVP
SVP
User avatar
G
Joined: 11 Sep 2015
Posts: 1911

Kudos [?]: 2757 [0], given: 364

Location: Canada
Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 03 Sep 2017, 06:54
Expert's post
Top Contributor
Bunuel wrote:
If \((3 + a)(\frac{a}{10} - 0.4) = -1\), then a could be

A. -4
B. -2
C. 1
D. 2
E. 4


Another approach is to eliminate the fractions/decimals first.

Given: (3 + a)(a/10 - 0.4) = -1
Multiply both sides by 10 to get: (3 + a)(a/10 - 0.4)(10) = (-1)(10)
Simplify: (3 + a)(a - 4) = -10
Expand and simplify: a² - a - 12 = -10
Add 10 to both sides: a² - a - 2 = 0
Factor: (a + 1)(a - 2) = 0

So, EITHER a = -1 OR a = 2

Answer:
[Reveal] Spoiler:
D


RELATED VIDEOS FROM OUR COURSE



_________________

Brent Hanneson – Founder of gmatprepnow.com

Image

Kudos [?]: 2757 [0], given: 364

Expert Post
Top Contributor
SVP
SVP
User avatar
G
Joined: 11 Sep 2015
Posts: 1911

Kudos [?]: 2757 [0], given: 364

Location: Canada
Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 03 Sep 2017, 06:57
Expert's post
Top Contributor
Bunuel wrote:
If \((3 + a)(\frac{a}{10} - 0.4) = -1\), then a could be

A. -4
B. -2
C. 1
D. 2
E. 4


Alternatively, once you get to the point where you have the equation (3 + a)(a - 4) = -10 [see my post above for how I got there], you could easily plug in the answer choices until you found the one that satisfies the equation (3 + a)(a - 4) = -10

Cheers,
Brent
_________________

Brent Hanneson – Founder of gmatprepnow.com

Image

Kudos [?]: 2757 [0], given: 364

Director
Director
User avatar
P
Joined: 04 Dec 2015
Posts: 696

Kudos [?]: 339 [0], given: 261

Location: India
Concentration: Technology, Strategy
Schools: ISB '19, IIMA , IIMB, XLRI
WE: Information Technology (Consulting)
GMAT ToolKit User CAT Tests
Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 03 Sep 2017, 07:02
Bunuel wrote:
If \((3 + a)(\frac{a}{10} - 0.4) = -1\), then a could be

A. -4
B. -2
C. 1
D. 2
E. 4

\((3 + a)(\frac{a}{10} - 0.4) = -1\)

\((3 + a)(\frac{a- 4}{10}) = -1\)

\((3 + a)(a- 4) = -10\)

\(3a -12 + a^2 - 4a = -10\)

\(a^2 - 4a + 3a -12 +10 = 0\)

\(a^2 - a -2 = 0\)

\((a -2)(a+1) = 0\)

\(a = 2\) or \(-1\)

Therefore "\(a\)" could be \(2\)

Answer (D)...

Kudos [?]: 339 [0], given: 261

Expert Post
Math Expert
User avatar
D
Joined: 02 Aug 2009
Posts: 5353

Kudos [?]: 6138 [0], given: 121

Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 01 Oct 2017, 09:45
Bunuel wrote:
If \((3 + a)(\frac{a}{10} - 0.4) = -1\), then a could be

A. -4
B. -2
C. 1
D. 2
E. 4



Hi...

if I want to do it fast and use logic..
\(\frac{a}{10}-0.4=\frac{a-4}{10}\)
so looking at the choices, 3+a should be a factor of 10...
A) so a could be -4 as \(3-4=-1\) but then the RHS will become positive so discard
B) a as -2 would make 3+a as 1 but \(\frac{a-4}{10}\) can never be -1
C) a as 1 gives 3+a as \(3+1=4\).. not a factor of 10.. Discard
D) a as 2 gives 3+a as \(3+2 = 5\), a factor of 10.. try substituting .. FITs in
E) a as 4 gives \(3+4=7\)... Discard

substitution this way would be way faster than finding solution of a
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 6138 [0], given: 121

Intern
Intern
avatar
Joined: 12 Feb 2017
Posts: 1

Kudos [?]: 0 [0], given: 2

Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 02 Oct 2017, 11:56
Simplifying the equation we get:
(3+a)(a/10-0.4)=-1
(3+a)(a-4)(1/10)=-1
(3+a)(a-4)=-10

Replacing a accoding to the choices:
A. -4 => (3-4)(-4-4) = -1*-8 =8 (Discard)
(...)
D. 2 => (3+2)(2-4) = 5*-2 = -10 (correct)

Kudos [?]: 0 [0], given: 2

Expert Post
Target Test Prep Representative
User avatar
S
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 1945

Kudos [?]: 1020 [0], given: 3

Location: United States (CA)
Re: If (3 + a)(a/10 - 0.4) = -1, then a could be [#permalink]

Show Tags

New post 04 Oct 2017, 15:46
Bunuel wrote:
If \((3 + a)(\frac{a}{10} - 0.4) = -1\), then a could be

A. -4
B. -2
C. 1
D. 2
E. 4


We can simplify the given equation:

(3 + a)(a/10 - 4/10) = -1

(3 + a)[(a-4)/10] = -1

(3 + a)(a - 4) = -10

a^2 - a - 12 = -10

a^2 - a - 2 = 0

(a - 2)(a + 1) = 0

a = 2 or a = -1

Answer: D
_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Kudos [?]: 1020 [0], given: 3

Re: If (3 + a)(a/10 - 0.4) = -1, then a could be   [#permalink] 04 Oct 2017, 15:46
Display posts from previous: Sort by

If (3 + a)(a/10 - 0.4) = -1, then a could be

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


GMAT Club MBA Forum Home| About| Terms and Conditions| 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®.