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

 It is currently 15 Oct 2019, 21:52

### 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

# If 0<b, and 0>ab, which of the following CANNOT be true?

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 58347
If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

15 Nov 2016, 09:49
1
3
00:00

Difficulty:

35% (medium)

Question Stats:

65% (01:34) correct 35% (01:47) wrong based on 171 sessions

### HideShow timer Statistics

If 0<b, and 0>ab, which of the following CANNOT be true?

A. (3b+5)/(1−a)>8
B. (a−1)/(3b+5)<8
C. (3b+5)/(a−1)<8
D. (3b+5)/(a−1)>8
E. (1−a)/(3b+5)>8

_________________
Intern
Joined: 29 Jun 2016
Posts: 6
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

15 Nov 2016, 10:01
i think that it should be D.

SOLUTION:
b can be any positive no. as given that b>0
and
a is always negative as ab < 0

So take any value of a and b, say a = -2 and b = 1.
the a -1 is always negative & since b > 0 so answer can't be B and C as they will be always negative.

and for E , 1-a will be positive and you can take any higher value of a and lower value of b.

similarly A will always be positive. but when you put any value in D , you get you will always get negative value. since a- 1 will be always negative. so it can't be greater than 8.

Senior Manager
Joined: 06 Jun 2016
Posts: 256
Location: India
Concentration: Operations, Strategy
Schools: ISB '18 (D)
GMAT 1: 600 Q49 V23
GMAT 2: 680 Q49 V34
GPA: 3.9
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

15 Nov 2016, 10:04
1
1
Bunuel wrote:
If 0<b, and 0>ab, which of the following CANNOT be true?

A. (3b+5)/(1−a)>8
B. (a−1)/(3b+5)<8
C. (3b+5)/(a−1)<8
D. (3b+5)/(a−1)>8
E. (1−a)/(3b+5)>8

D

b>0 (b is positive) ab<0 (a is negative)

A. (3b+5)/(1−a)>8 positive/positive=positive can be true
B. (a−1)/(3b+5)<8 negative/positive=negative can be true
C. (3b+5)/(a−1)<8 positive/negative=negative can be true
D. (3b+5)/(a−1)>8 positive/negative= negative cannot be true
E. (1−a)/(3b+5)>8 positive/positive=positive can be true
Status: Preparing for GMAT
Joined: 25 Nov 2015
Posts: 1043
Location: India
GPA: 3.64
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

15 Nov 2016, 10:09
0<b implies b is positive
0>ab implies a is negative
A. (3b+5)/(1−a)>8 - Both numerator and denominator is positive, so possible

B. (a−1)/(3b+5)<8 - Numerator negative but denominator positive, so possible.

C. (3b+5)/(a−1)<8 - Numerator positive but denominator negative, so possible.

D. (3b+5)/(a−1)>8 - Numerator positive but denominator negative, so not possible to be >8.

E. (1−a)/(3b+5)>8 - Both numerator and denominator is positive, so possible

If u liked my post, press kudos!

_________________
Please give kudos, if you like my post

When the going gets tough, the tough gets going...
Target Test Prep Representative
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2817
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

17 Nov 2016, 14:50
Bunuel wrote:
If 0<b, and 0>ab, which of the following CANNOT be true?

A. (3b+5)/(1−a)>8
B. (a−1)/(3b+5)<8
C. (3b+5)/(a−1)<8
D. (3b+5)/(a−1)>8
E. (1−a)/(3b+5)>8

Since 0 < b and 0 > ab, b must be positive and ab must be negative. If b is positive and ab is negative, then a must be negative. We need to determine which of the answer choices cannot be true.

Since each of the choices has at least one of the quantities 3b + 5, 1 - a, and a - 1, we can analyze whether those quantities are positive or negative.

Since b is positive, 3b + 5 is positive.

Since a is negative, 1 - a is positive.

Since a is negative, a - 1 is negative.

Now, let’s analyze each answer choice.

A) (3b+5)/(1−a) is the quotient between two positive quantities, so it must be positive and can be greater than 8.

B) (a−1)/(3b+5) is the quotient between a negative quantity and a positive quantity, so it must be negative and thus less than 8.

C) (3b+5)/(a−1) is the quotient between a positive quantity and a negative quantity, so it must be negative and thus less than 8.

D) By our analysis in answer choice C, we know that (3b+5)/(a−1) is negative; therefore (3b+5)/(a−1) is NOT greater than 8.

_________________

# Jeffrey Miller

Jeff@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Manager
Joined: 15 Jan 2019
Posts: 60
Location: India
GMAT 1: 650 Q42 V38
GPA: 4
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

18 Sep 2019, 08:38
Bunuel wrote:
If 0<b, and 0>ab, which of the following CANNOT be true?

A. (3b+5)/(1−a)>8
B. (a−1)/(3b+5)<8
C. (3b+5)/(a−1)<8
D. (3b+5)/(a−1)>8
E. (1−a)/(3b+5)>8

is the best approach for question is to attempt each option individually? or can we try any other approach
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 8069
Location: United States (CA)
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

23 Sep 2019, 09:35
Bunuel wrote:
If 0<b, and 0>ab, which of the following CANNOT be true?

A. (3b+5)/(1−a)>8
B. (a−1)/(3b+5)<8
C. (3b+5)/(a−1)<8
D. (3b+5)/(a−1)>8
E. (1−a)/(3b+5)>8

Since b is positive, a must be negative so that ab < 0.

Since (3b + 5) is positive, (1 - a) is positive, and (a - 1) is negative, the fractions in choices A, B, and E are positive and the fractions in choices C and D are negative. We see that D cannot be true.

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Manager
Joined: 20 Apr 2019
Posts: 92
Re: If 0<b, and 0>ab, which of the following CANNOT be true?  [#permalink]

### Show Tags

24 Sep 2019, 02:20
Actually, just by looking at the answer choices, we see that C and D are exactly the same just with reverse signs. Therefore, we could conclude that one of them must be incorrect.
Re: If 0<b, and 0>ab, which of the following CANNOT be true?   [#permalink] 24 Sep 2019, 02:20
Display posts from previous: Sort by