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

 It is currently 16 Jul 2018, 13:33

### 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 5^21 X 4^11 = 2 X 10^n, what is the valve of n?

 post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
Manager
Joined: 05 Aug 2008
Posts: 88
Schools: McCombs Class of 2012
If 5^21 X 4^11 = 2 X 10^n, what is the valve of n? [#permalink]

### Show Tags

17 Dec 2008, 16:53
If $$5^2^1 X 4^1^1 = 2 X 10^n$$, what is the valve of n?

(A) 11
(B) 21
(C) 22
(D) 23
(E) 32

E is correct

anyone please give an approach to how they solved this problem (problem attached as image).

thanks.

Ops -- sorry wrong place!

--== 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.

Attachments

Q1.JPG [ 14.24 KiB | Viewed 876 times ]

Intern
Joined: 17 Dec 2008
Posts: 20

### Show Tags

17 Dec 2008, 18:30
I got stuck on this one as well.

The way it was explained is:

5^21 x 4^21 = 2 x 10^n

1. Notice that 4^21 can be factored as 2 x 2^21
2. Bases with the same exponent can be multiplied together, keeping the same exponent (5x2 = 10 ... add the exponent back 10^21)
3. That leaves you with 2 (that you factored out from step 1) and 10^21 AKA

2 x 10^21

Retired Moderator
Joined: 05 Jul 2006
Posts: 1734

### Show Tags

18 Dec 2008, 00:28
5^21 * 4^11 = 2* 10^n

5^21*2^21*2 = 2*10^n,

(5*2)^21 = 10^n

10^21 = 10^n

n = 21

--== 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] 18 Dec 2008, 00:28
Display posts from previous: Sort by

# If 5^21 X 4^11 = 2 X 10^n, what is the valve of n?

 post reply Question banks Downloads My Bookmarks Reviews Important topics

Moderator: chetan2u

# Events & Promotions

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.