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

 It is currently 18 Jun 2018, 08:43

### 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

# If 4^4x = 1600, what is the value of (4^(x 1))^2? 40 20 10

Author Message
Senior Manager
Joined: 05 Oct 2008
Posts: 258
If 4^4x = 1600, what is the value of (4^(x 1))^2? 40 20 10 [#permalink]

### Show Tags

Updated on: 11 Dec 2008, 09:02
If 4^4x = 1600, what is the value of (4^(x–1))^2?

40
20
10
5/2
5/4

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

Originally posted by study on 11 Dec 2008, 02:45.
Last edited by study on 11 Dec 2008, 09:02, edited 1 time in total.
Manager
Joined: 14 Oct 2008
Posts: 158

### Show Tags

11 Dec 2008, 03:13
Please post the question correctly. I guess the qs is

4^(x-1)^2 i.e 4^(2x-2)
In which case the answer should be D

4^4x = 1600
take root of both sides
4^2x = 40

Substitute the value in the qs

4^2x / 4^2
40/16 = 5/2

If its the way you have printed the qs (4^x - 1 )^2
then 4^x = sqrt(40)

hence (4^x - 1 )^2 =
4^(2x) - 2*4^(x) + 1
40 - 2* sqrt(40) + 1
41 - 2* sqrt(40)
The value is between 27 and 29 , it cannot be evaluated into any given answers .
Senior Manager
Joined: 05 Oct 2008
Posts: 258

### Show Tags

11 Dec 2008, 09:04
i just copy pasted the problem from the source.
Senior Manager
Joined: 30 Nov 2008
Posts: 479
Schools: Fuqua

### Show Tags

12 Dec 2008, 12:58
I would go with D - 5/2 . Here is my explanation.

(4 ^ (x-1)) ^2 = ?

Above equation is same = 4 ^ (2x-2) ==> 4 ^2x / 4 ^2 -----Eq 1

Given 4 ^ 4x = 1600 ==> (4 ^2x) ^2 = 1600 ---> Eq 2

Take the SQRT on both sides in Eq 2
==> 4 ^ 2x = 40

Replacing 4 ^2 in eq 1, we get 40 / 4 ^ 2 ==> 40 / 26 ==> 5/2

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: Exponents   [#permalink] 12 Dec 2008, 12:58
Display posts from previous: Sort by