Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 23 Nov 2014, 09:08

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# DS: Value of a

Author Message
TAGS:
Senior Manager
Joined: 02 Oct 2005
Posts: 305
Followers: 1

Kudos [?]: 5 [0], given: 0

DS: Value of a [#permalink]  19 Nov 2005, 17:15
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
Attachments

PR3_Q37.JPG [ 6.2 KiB | Viewed 483 times ]

SVP
Joined: 05 Apr 2005
Posts: 1734
Followers: 4

Kudos [?]: 34 [0], given: 0

Re: DS: Value of a [#permalink]  19 Nov 2005, 17:46
i) a = -3, 4
ii) b = -1, 2
from i and ii, a = 4 b = -1.
Senior Manager
Joined: 02 Oct 2005
Posts: 305
Followers: 1

Kudos [?]: 5 [0], given: 0

Re: DS: Value of a [#permalink]  19 Nov 2005, 19:07
HIMALAYA wrote:
i) a = -3, 4
ii) b = -1, 2
from i and ii, a = 4 b = -1.

Could you please show it working?
SVP
Joined: 24 Sep 2005
Posts: 1898
Followers: 11

Kudos [?]: 113 [0], given: 0

Re: DS: Value of a [#permalink]  19 Nov 2005, 19:27
HIMALAYA wrote:
i) a = -3, 4
ii) b = -1, 2
from i and ii, a = 4 b = -1.

a^2-a=12--->a^2-a-12=0 ---> (a-4)(a+3)= 0 ---> a=-3,4
b^2-b=2---> b^2-b-2= 0 ---> (b-2)(b+1)=0 ---> b=-1,2
now look at the square root, quickly you can eliminate a=-3 , becoz a^3 is the biggest power and the determinant of the value of the squareroot, if a=-3, the value inside the sqrt<0 ---> undefined.
Test a=4, try b=-1 , yeah, that's it!
try b=2, no.

----> a=4, b=-1
Senior Manager
Joined: 02 Oct 2005
Posts: 305
Followers: 1

Kudos [?]: 5 [0], given: 0

Do you guys say the answer is C? The OA is B, but I don't know how to conclude that.
SVP
Joined: 24 Sep 2005
Posts: 1898
Followers: 11

Kudos [?]: 113 [0], given: 0

okie, let's see:
from 2, we obtain b=4 or -1
that is to say : the square root can be 7^2+(-1) (= 48) or 7^2+ 2(=51)

case 1:
we have a^3-a^2 = 48
---> a^3 + 3a^2- 4a^2 + 12a -12a -48= 0 ( this is a high school's method to factorize the expression to obtain an equation with RHS= 0)
---> a^2(a-4) + 3a(a-4) +12(a-4)= 0
----> (a-4) * ( a^2+3a+12)=0
-----> a=4, a^2 + 3a +12 has no solution since delta<0 ( quadratic equation method)

case 2 : a^3- a^2= 51 or a^3-a^2-51=0
since a must be an integer ---> the possible roots of this equation must be among factors of 51 ( +-17 and +- 3) . You can plug these numbers to see if they're roots of the equation . NOTE: Better method to plug is to right away notice that the root can't be negative because the highest power of a here, a^3 determine the value of LHS. After plugging, you find that there's no root for this equation.

Thus, the only value of a obtained is 4 when b=-1

Thus, B is correct!
VP
Joined: 30 Sep 2004
Posts: 1493
Location: Germany
Followers: 4

Kudos [?]: 58 [0], given: 0

sudhagar wrote:
Do you guys say the answer is C? The OA is B, but I don't know how to conclude that.

this is a good question ! what is the source of it ?
_________________

If your mind can conceive it and your heart can believe it, have faith that you can achieve it.

SVP
Joined: 28 May 2005
Posts: 1743
Location: Dhaka
Followers: 6

Kudos [?]: 55 [0], given: 0

very good question. almost got this one wrong.
_________________

hey ya......

Current Student
Joined: 28 Dec 2004
Posts: 3399
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 13

Kudos [?]: 172 [0], given: 2

got blown away on this one...

now I see why it is B...lexi nice job!
Similar topics Replies Last post
Similar
Topics:
ds absolute values 8 27 Feb 2006, 22:38
inequality/abs value ds 2 16 Jan 2006, 01:44
Ds absolute value 4 06 Oct 2005, 00:25
DS - What is the value of b? 5 18 Sep 2005, 07:23
ds: abs value 22 06 Apr 2005, 12:35
Display posts from previous: Sort by