exponents.....

Expert replies

vaswani.sharan: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Tue Apr 10, 2012 10:18 am

by vaswani.sharan » Sun Apr 15, 2012 10:53 am

Hey, just getting my math feet back under me, I am not so bad at exponents, but this question is bugging me. Not sure how I could quickly solve it.
can some one show me a fast way?

(5^21)(4^11)=2x10^n
n=21

Like this post

Source: Beat The GMAT — Problem Solving | Sun Apr 15, 2012 10:53 am

shubham_k: Junior | Next Rank: 30 Posts; Posts: 27; Joined: Sun Apr 08, 2012 5:38 am; Thanked: 20 times

by shubham_k » Sun Apr 15, 2012 11:00 am

We see "5" and "4" on the left side and "10" on the right side.. somehow we want to make the bases the same.

So, let's start by turning the "4" into "2^2":

(5^21)((2^2)^11) = 2*10^n

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

Now, we want to be able to simplify the left side, but we can only do so if the exponents are equal, so:

(5^21)(2^21)(2^1) = 2*10^n

if we divide both sides by 2, we get:

(5^21)(2^21) = 10^n

and since the exponents are equal on the left side, we can say:

(5*2)^21 = 10^21

and finally

10^21 = 10^n

so 21 = n.

Not a difficult one i guess.....

Like this post

Shalabh's Quants: Master | Next Rank: 500 Posts; Posts: 134; Joined: Fri Apr 06, 2012 3:11 amFollowed by: 5 members; Thanked: 35 times

by Shalabh's Quants » Sun Apr 15, 2012 12:10 pm

vaswani.sharan wrote:Hey, just getting my math feet back under me, I am not so bad at exponents, but this question is bugging me. Not sure how I could quickly solve it.
can some one show me a fast way?

(5^21)(4^11)=2x10^n
n=21

Lets break it into prime factors...

(5^21)(4^11)=2x10^n

5^21*(2^2)^11=2*(2.5)^n

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

5^21*2^22 = 2^(n+1).5^n

Either equate exponents of 2 or 5. Both gives n = 21.

Shalabh Jain,
e-GMAT Instructor

Like this post

GMAT/MBA Expert

Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Sun Apr 15, 2012 5:21 pm

vaswani.sharan wrote:Hey, just getting my math feet back under me, I am not so bad at exponents, but this question is bugging me. Not sure how I could quickly solve it.
can some one show me a fast way?

(5^21)(4^11)=2x10^n
n=21

(5^21)(4^11) = 2 x 10^n
(5^21)(2^2)^11 = 2 x (2 * 5)^n
(5^21)(2^22) = 2 x 2^n * 5^n
(5^21)(2^22) = 2^(n + 1) * 5^n
Now since the bases are the same, so exponents will also be the same on both sides.
So, n = 21

Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review