BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Inequalities - GT & LT

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 2109
Joined: Sun Apr 19, 2009 10:25 pm
Location: New Jersey
Thanked: 109 times
Followed by:79 members
GMAT Score:640

Inequalities - GT & LT

by money9111 » Sat Feb 13, 2010 5:29 pm
If (a^2)b>1 and b<2, which of the following could be the value of a?

a. 1/2
b. 1/4
c. -(1/2)
d. -2
e. 2/3

Answer is D

this question is from the MGMAT Equations, Inequalities, & VIC's. The explanation in the book is confusing because it uses the GT and LT, which are Greater than and Less than... my question is how do you know when to switch from GT to LT?
My goal is to make MBA applicants take onus over their process.

My story from Pre-MBA to Cornell MBA - New Post in Pre-MBA blog

Me featured on Poets & Quants

Free Book for MBA Applicants

Top
Source: — Problem Solving |
User avatar
Community Manager
Posts: 1537
Joined: Mon Aug 10, 2009 6:10 pm
Thanked: 653 times
Followed by:252 members

by papgust » Sat Feb 13, 2010 7:26 pm
I felt that backsolving is best and easy way for this question.

A. 1/2
1/4 * b > 1. This means that b must be > 4. But b < 2 in the question. Eliminate

B. 1/4
1/16 * b > 1. This means that b must be > 16. But b < 2 in the question. Eliminate

C. -1/2
1/4 * b > 1. This means that b must be > 4. But b < 2 in the question. Eliminate

D. -2
4 * b > 1. This means that b must be < 1 and satisfies b < 2 in the question. Correct

E. 2/3
4/9 * b > 1. This means that b must be > 9/4. But b < 2 in the question. Eliminate.
Last edited by papgust on Mon Feb 15, 2010 11:45 pm, edited 1 time in total.
Top
User avatar
Legendary Member
Posts: 2109
Joined: Sun Apr 19, 2009 10:25 pm
Location: New Jersey
Thanked: 109 times
Followed by:79 members
GMAT Score:640

by money9111 » Sat Feb 13, 2010 8:12 pm
ok i didn't think to backsolve... i don't know if i like how the MGMAT guide explains it using GT and LT... but I think i'll be able to get it... it's just uncomfortable now
My goal is to make MBA applicants take onus over their process.

My story from Pre-MBA to Cornell MBA - New Post in Pre-MBA blog

Me featured on Poets & Quants

Free Book for MBA Applicants

Top
Master | Next Rank: 500 Posts
Posts: 177
Joined: Sun Aug 02, 2009 9:39 pm
Thanked: 6 times

by okigbo » Sun Feb 14, 2010 7:59 am
I too don't like the GT and LT approach of the mgmat books.

I just reasoned it out. a^2 will be positive no matter what and since the solution is greater than 1, and we know that b is less than 2, b MUST equal 1. Therefore, the equation becomes a^2>1; which means a >1 or a<-1. Pick D and move on...
Top
User avatar
Legendary Member
Posts: 2109
Joined: Sun Apr 19, 2009 10:25 pm
Location: New Jersey
Thanked: 109 times
Followed by:79 members
GMAT Score:640

by money9111 » Sun Feb 14, 2010 12:05 pm
Lol okigbo I agree... Just move on and don't look back! Thanks guys for your explanations!
My goal is to make MBA applicants take onus over their process.

My story from Pre-MBA to Cornell MBA - New Post in Pre-MBA blog

Me featured on Poets & Quants

Free Book for MBA Applicants

Top
User avatar
Legendary Member
Posts: 1022
Joined: Mon Jul 20, 2009 11:49 pm
Location: Gandhinagar
Thanked: 41 times
Followed by:2 members

by shashank.ism » Mon Feb 15, 2010 11:54 am
money9111 wrote:If (a^2)b>1 and b<2, which of the following could be the value of a?

a. 1/2
b. 1/4
c. -(1/2)
d. -2
e. 2/3

Answer is D

this question is from the MGMAT Equations, Inequalities, & VIC's. The explanation in the book is confusing because it uses the GT and LT, which are Greater than and Less than... my question is how do you know when to switch from GT to LT?
I couldn't understand the question. what does it exactly mean???
My Websites:
www.mba.webmaggu.com - India's social Network for MBA Aspirants

www.deal.webmaggu.com -India's online discount, coupon, free stuff informer.

www.dictionary.webmaggu.com - A compact free online dictionary with images.

Nothing is Impossible, even Impossible says I'm possible.
Top
User avatar
Legendary Member
Posts: 1132
Joined: Mon Jul 20, 2009 3:38 am
Location: India
Thanked: 64 times
Followed by:6 members
GMAT Score:760

by harsh.champ » Mon Feb 15, 2010 11:10 pm
papgust wrote:I felt that backsolving is best and easy way for this question.

A. 1/2
1/4 * b > 1. This means that b must be > 4. But b < 2 in the question. Eliminate

B. 1/4
1/16 * b > 1. This means that b must be > 16. But b < 2 in the question. Eliminate

C. -1/2
1/4 * b > 1. This means that b must be > 4. But b < 2 in the question. Eliminate

D. -2
4 * b > 1. This means that b must be < 1 and satisfies b < 2 in the question. Correct

E. 1/2
1/4 * b > 1. This means that b must be > 4. But b < 2 in the question. Eliminate
Hey papgust,
I think in order to solve quickly u took the wrong E option.E is "2/3" not "1/2".Anyways ,still we are getting b>2 by plugging a=2/3 ,but still ,had it been some other no. it could have spelled trouble.

Over here,putting a=2/3
(4/9)*b>1
i.e. b>9/4[GT does not change to LT as 4/9 is +ve and transposing it wouldn't affect the inequality sign]
which is not possible as b<2 in the question.Hence ,E can be eliminated.
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



Just because something is hard doesn't mean you shouldn't try,it means you should just try harder.

"Keep Walking" - Johnny Walker :P
Top
User avatar
Legendary Member
Posts: 1132
Joined: Mon Jul 20, 2009 3:38 am
Location: India
Thanked: 64 times
Followed by:6 members
GMAT Score:760

by harsh.champ » Mon Feb 15, 2010 11:20 pm
money9111 wrote:If (a^2)b>1 and b<2, which of the following could be the value of a?

a. 1/2
b. 1/4
c. -(1/2)
d. -2
e. 2/3

Answer is D

this question is from the MGMAT Equations, Inequalities, & VIC's. The explanation in the book is confusing because it uses the GT and LT, which are Greater than and Less than... my question is how do you know when to switch from GT to LT?
The basic rule to be kept in mind:- In addition and subtraction,the GT and LT signs will never change.
Ex:-3>2
3 + 5 > 2 + 5

or 11 < 13
-8 +11 < -8 +13

However in multiplication and division,if a -ve no. is multiplied with,then LT would change to GT and vice-versa.
Ex:- 3>2
(-1) x 3 < (-1) x 2 [-3 < -2]

Similarly it goes for division:-
6 > 2
Dividing by -2
6/-2 < 2/-2 (-3 < -1)

I hope this clears your doubts.:)
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



Just because something is hard doesn't mean you shouldn't try,it means you should just try harder.

"Keep Walking" - Johnny Walker :P
Top
User avatar
Community Manager
Posts: 1537
Joined: Mon Aug 10, 2009 6:10 pm
Thanked: 653 times
Followed by:252 members

by papgust » Mon Feb 15, 2010 11:46 pm
harsh.champ wrote: Hey papgust,
I think in order to solve quickly u took the wrong E option.E is "2/3" not "1/2".Anyways ,still we are getting b>2 by plugging a=2/3 ,but still ,had it been some other no. it could have spelled trouble.
Thank you for pointing it out. I've edited now.
Top
Post new topic Post Reply
• Page 1 of 1