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

 It is currently 21 Jun 2018, 08:45

### 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

# Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 46251
Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12 [#permalink]

### Show Tags

07 May 2018, 02:51
00:00

Difficulty:

25% (medium)

Question Stats:

76% (01:55) correct 24% (00:48) wrong based on 72 sessions

### HideShow timer Statistics

Is ab negative?

(1) $$ab^8 < 0$$

(2) $$a + b^8 = 12$$

_________________
Manager
Joined: 09 Aug 2017
Posts: 96
Re: Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12 [#permalink]

### Show Tags

07 May 2018, 04:04
Statement 1
a*b^8 < 0
implies that a is negative but doesn't tell us about b so insufficient.

Statement 2
a+b^8= 12
Nothing is clear form this statement.
Insufficient.

St.1 + st. 2
Still not clear.

Intern
Joined: 05 Jan 2014
Posts: 43
GMAT 1: 610 Q47 V26
WE: Information Technology (Computer Software)
Re: Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12 [#permalink]

### Show Tags

07 May 2018, 07:31
1
IMO A.

1. a*(b^8) < 0. b^8 will be positive. Hence, 'a' will be -ve. Sufficient
2. In this case, 'a' can be -ve or +ve depending upon magnitude of b^8. Insufficient
Intern
Joined: 13 Mar 2018
Posts: 2
Re: Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12 [#permalink]

### Show Tags

07 May 2018, 08:14
gvij2017 wrote:
Statement 1
a*b^8 < 0
implies that a is negative but doesn't tell us about b so insufficient.

Statement 2
a+b^8= 12
Nothing is clear form this statement.
Insufficient.

St.1 + st. 2
Still not clear.

In statement 1, we know for sure that b is positive because of the even power of b. And for the whole thing to be less than 0. A has to be negative. Therefore, sufficient
Hence, option A is correct choice

Sent from my iPhone using GMAT Club Forum mobile app
Intern
Joined: 27 Nov 2016
Posts: 45
Location: India
Schools: ISB '19
GPA: 2.75
Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12 [#permalink]

### Show Tags

07 May 2018, 09:41
nehakhetan88 and NonPlus

Statement 1 is not sufficient because "a" is negative we know, but coming back to question at hand that whether ab<0 lets consider this.
a is -ve but when b is +ve, we get ab<0
but when a is -ve and b is also -ve, then ab>0
So, Just because b^8 is +ve we cant comment on the nature of b. b can either be +ve or -ve.

Statement 2 is also not sufficient.
a + b^8 = 12. In this, we will have break points when b is 1 or 2 or -2 etc.
When b is 1, a is +ve but when b is -2, a is -ve. So even in this case we are not clear. Hence insufficient.

Taking Statement 1 and 2 together.

In this we rule out all the cases where a is +ve. Just take a -ve since thats what we got from statement 1.
Now, a can be -ve when b is 3, -3, 2, -10 etc.
Hence even after taking both the statements we cant tell whether ab is <0.

_________________

Please appreciate with a kudo if my post is helpful to you

Intern
Joined: 28 Nov 2017
Posts: 2
Re: Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12 [#permalink]

### Show Tags

13 Jun 2018, 14:26
Statement 1 : $$ab^8<0$$

Here $$b^8$$ irrespective of b being negative or positive will be positive.
Hence, we can conclude a is negative. But we don't know anything about b.
If b is positive then ab is negative; but if b is negative ab will be positive.
Not sufficient

Statement 2 : $$a+b^8 = 12$$
Again b^8 will be positive and a can be negative or positive, suppose b is positive and a is negative but less than b
Then outcome will be positive. Also a can be positive and $$a+b^8$$ will sum up to 12.
Not sufficient

Also Stmt 1 & 2 together doesn't reflect whether b is negative or positive as $$b^8$$ will always be positive.

Please hit Kudos if this post in anyway helps you
Re: Is ab negative? (1) ab^8 < 0 (2) a + b^8 = 12   [#permalink] 13 Jun 2018, 14:26
Display posts from previous: Sort by