It is currently 20 Oct 2017, 15:24

### 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

# The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 41892

Kudos [?]: 129030 [0], given: 12187

The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

01 Aug 2017, 01:18
Expert's post
2
This post was
BOOKMARKED
00:00

Difficulty:

45% (medium)

Question Stats:

67% (01:10) correct 33% (01:31) wrong based on 113 sessions

### HideShow timer Statistics

The equation $$n < \frac{1}{{(-2)^{-n}}} < 135.43$$ is true for how many unique integer values of n, where n is a prime number?

A. 7
B. 4
C. 2
D. 1
E. 0
[Reveal] Spoiler: OA

_________________

Kudos [?]: 129030 [0], given: 12187

Director
Joined: 18 Aug 2016
Posts: 512

Kudos [?]: 140 [1], given: 123

GMAT 1: 630 Q47 V29
Re: The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

01 Aug 2017, 01:53
1
KUDOS
Bunuel wrote:
The equation $$n < \frac{1}{{(-2)^{-n}}} < 135.43$$ is true for how many unique integer values of n, where n is a prime number?

A. 7
B. 4
C. 2
D. 1
E. 0

$$n < \frac{1}{{(-2)^{-n}}} < 135.43$$
n has to be + as NO negative numbers are prime nos. Hence (-2)^n should also be positive
only even values of n can yield positive result
Only even prime number is 2. Hence n can take only 1 value i.e. 2
D
_________________

We must try to achieve the best within us

Thanks
Luckisnoexcuse

Kudos [?]: 140 [1], given: 123

Manager
Joined: 20 Aug 2015
Posts: 65

Kudos [?]: 9 [0], given: 149

GMAT 1: 710 Q50 V36
Re: The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

05 Aug 2017, 09:02
1
This post was
BOOKMARKED
Bunuel wrote:
The equation $$n < \frac{1}{{(-2)^{-n}}} < 135.43$$ is true for how many unique integer values of n, where n is a prime number?

A. 7
B. 4
C. 2
D. 1
E. 0

$$n < \frac{1}{{(-2)^{-n}}} < 135.43$$

n < (-2)^n < 135.43

Since n is a prime number, by putting numbers-
n=2, 2< 4< 135.43
For n=3,5,7 the equation doesn't hold

So, ans is D) 1.

Kudos [?]: 9 [0], given: 149

Intern
Joined: 05 Dec 2015
Posts: 4

Kudos [?]: 7 [0], given: 9

Location: Brazil
GMAT 1: 720 Q50 V38
WE: Investment Banking (Investment Banking)
The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

05 Aug 2017, 17:37
The expression n < 1/(-2)^(-n) < 135.43 is equivalent to n < $$(-2)^{n}$$ < 135.43

For n=2: 2 < 4 < 135.43 OK
For n=3: 3 < -27 < 135.43 NOT OK
For n=5: 5 < -32 < 135.43 NOT OK
For n=7: 7 < -128 < 135.43 NOT OK

Since 2 is the only even prime number, we didn't even have to test the other cases (n=3,5,7, etc.)

_________________

_________________
If you find my post helpful, please give kudos. Help me unlock the GMAT Club tests.

Last edited by lukera on 08 Aug 2017, 07:37, edited 2 times in total.

Kudos [?]: 7 [0], given: 9

Manager
Status: love the club...
Joined: 24 Mar 2015
Posts: 175

Kudos [?]: 14 [0], given: 413

Re: The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

08 Aug 2017, 03:44
lukera wrote:
The expression n < 1/(-2)^(-n) < 135.43 is equivalent to n < $$(-2)^{n}$$ < 135.43

For n=2: 2 < 4 < 135.43 OK
For n=3: 2 < -27 < 135.43 NOT OK
For n=5: 2 < -32 < 135.43 NOT OK
For n=7: 2 < -128 < 135.43 NOT OK

Since 2 is the only even prime number, we didn't even have to test the other cases (n=3,4,5, etc.)

hey

???

you have plugged prime values such as 3,5 , and 7, but you didn't put the values in place of "n" ...
why....?

Kudos [?]: 14 [0], given: 413

Intern
Joined: 05 Dec 2015
Posts: 4

Kudos [?]: 7 [0], given: 9

Location: Brazil
GMAT 1: 720 Q50 V38
WE: Investment Banking (Investment Banking)
Re: The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

08 Aug 2017, 07:38
ssislam wrote:
lukera wrote:
The expression n < 1/(-2)^(-n) < 135.43 is equivalent to n < $$(-2)^{n}$$ < 135.43

For n=2: 2 < 4 < 135.43 OK
For n=3: 2 < -27 < 135.43 NOT OK
For n=5: 2 < -32 < 135.43 NOT OK
For n=7: 2 < -128 < 135.43 NOT OK

Since 2 is the only even prime number, we didn't even have to test the other cases (n=3,4,5, etc.)

hey

???

you have plugged prime values such as 3,5 , and 7, but you didn't put the values in place of "n" ...
why....?

I did ctrl C and ctrl V and forgot to update the values, thanks for the reminder
_________________

_________________
If you find my post helpful, please give kudos. Help me unlock the GMAT Club tests.

Kudos [?]: 7 [0], given: 9

Manager
Status: love the club...
Joined: 24 Mar 2015
Posts: 175

Kudos [?]: 14 [0], given: 413

Re: The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in [#permalink]

### Show Tags

08 Aug 2017, 09:59
lukera wrote:
ssislam wrote:
lukera wrote:
The expression n < 1/(-2)^(-n) < 135.43 is equivalent to n < $$(-2)^{n}$$ < 135.43

For n=2: 2 < 4 < 135.43 OK
For n=3: 2 < -27 < 135.43 NOT OK
For n=5: 2 < -32 < 135.43 NOT OK
For n=7: 2 < -128 < 135.43 NOT OK

Since 2 is the only even prime number, we didn't even have to test the other cases (n=3,4,5, etc.)

hey

???

you have plugged prime values such as 3,5 , and 7, but you didn't put the values in place of "n" ...
why....?

I did ctrl C and ctrl V and forgot to update the values, thanks for the reminder

hahahaha
I got it ...

thanks

Kudos [?]: 14 [0], given: 413

Re: The equation n < 1/(-2)^(-n) < 135.43 is true for how many unique in   [#permalink] 08 Aug 2017, 09:59
Display posts from previous: Sort by