Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 27 Mar 2015, 18:23

### 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

# Exponent problem

Author Message
TAGS:
Intern
Joined: 09 Jan 2007
Posts: 24
Followers: 0

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

Exponent problem [#permalink]  06 Feb 2007, 16:21
If 5^21X4^11=2X10^n, what is n?

11
21
22
23
32

The answer is 21, but why? Step by step please. Thank you.
Manager
Joined: 22 Feb 2004
Posts: 60
Location: Florida
Followers: 1

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

I'm no math expert, but here is how I did it.

The first thing I did was rename 4^21 as 2^22. This is because 4=2^2 and you multiply the exponents.

The second step was to divide both sides by 2, to get 5^21 * 2^21 = 10^n

When I saw this I realized that what you're saying is you have 21 groups of 5 and 21 groups of 2. Since 5 * 2=10, you have 21 groups of 10 or 10^21.

I don't know if there is an exponent rule for the last step, but that's how I solved it.
Intern
Joined: 09 Jan 2007
Posts: 24
Followers: 0

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

Thanks for the explanation
SVP
Joined: 05 Jul 2006
Posts: 1522
Followers: 5

Kudos [?]: 107 [0], given: 39

If 5^21X4^11=2X10^n, what is n?

11
21
22
23
32

5^21 * 2^22 -1 = 2^n*5*n

thus 2^21 = 2^n , n = 21
Similar topics Replies Last post
Similar
Topics:
11 Exponents Problem (m04q20) 21 19 Jun 2007, 19:15
GMATPrep 2: exponent problem 4 07 Jul 2007, 18:31
Exponents Problem solution 2 11 Mar 2007, 15:21
Exponent Problem (simple) 3 02 Jan 2007, 21:31
exponent problem 3 23 Mar 2006, 19:43
Display posts from previous: Sort by