BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Algebra question

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Sun Aug 03, 2008 5:27 pm

Algebra question

by blueland78 » Sun Aug 03, 2008 5:34 pm
5^21 * 4^11 = 2 * 10^n what is n?

a) 11
b)21
c)22
d)23
e)32

came across this problem while doing gmat prep exam that I downloaded.
how would you go about solving this????
SJ
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 222
Joined: Fri Jan 04, 2008 8:10 pm
Thanked: 15 times

by sibbineni » Sun Aug 03, 2008 5:53 pm
5^21 * 4^11 = 2 * 10^n

5^21*2^22=2 * 10^n

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

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

(5*2)^21=10^n

10^21=10^n

as bases are equal equating the exponents

n=21

IMO B
Top
Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Sun Aug 03, 2008 5:27 pm

hmm

by blueland78 » Sun Aug 03, 2008 9:48 pm
what ever happened to 2^21 at the second to last step????
I cant see it..@.@
SJ
Top
Legendary Member
Posts: 661
Joined: Tue Jul 08, 2008 12:58 pm
Location: France
Thanked: 48 times

by pepeprepa » Mon Aug 04, 2008 1:41 am
To go from this one to the other:
2*5^21*2^21=2*10^n
(5*2)^21=10^n
You have to know that k^a*m^a=(km)^a
Look at your math review.
Top
Master | Next Rank: 500 Posts
Posts: 222
Joined: Fri Jan 04, 2008 8:10 pm
Thanked: 15 times

by sibbineni » Mon Aug 04, 2008 3:07 am
2*5^21*2^21=2*10^n

5^21*2^21=10^n
here by applying the following formula a^n*b^n=(ab)^n

(5*2)^21=10^n

10^21=10^n
Top
Post new topic Post Reply
• Page 1 of 1