Reducing Powers

Expert replies

lukeposada: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Tue Jul 20, 2010 12:02 pm

by lukeposada » Sun Aug 01, 2010 3:29 pm

Need some help understanding this one:

The value of (10^8 - 10^2)/(10^7 - 10^3) is closest to which of the following?

a - 1
b - 10
c - 10^2
d - 10^3
e - 10^4

the answer is b

Like this post

Source: Beat The GMAT — Problem Solving | Sun Aug 01, 2010 3:29 pm

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Sun Aug 01, 2010 4:03 pm

lukeposada wrote:Need some help understanding this one:

The value of (10^8 - 10^2)/(10^7 - 10^3) is closest to which of the following?
a - 1
b - 10
c - 10^2
d - 10^3
e - 10^4
the answer is b

It's important to note that the question asks us to to find the closest value here.

The fast approach is to recognize that 10^8 (100 billion) is wayyyyyyyyyyy larger than 10^2 (100). In fact 10^2 is quite insignificant compared to 10^8

So, 10^8 - 10^2 is pretty close in value to 10^8 (Aside: If you had $100 billion dollars and you lost $100 dollars, you still pretty much have $100 billion dollars)

The same applies to 10^7 - 10^3 (10^7=10 billion, and 10^3=1000). So, 10^7 - 10^3 is pretty close to 10^7

So, (10^8 - 10^2)/(10^7 - 10^3) is very close to (10^8)/(10^7) and (10^8)/(10^7) = 10^1 = 10

Choose B.

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Sun Aug 01, 2010 4:27 pm

lukeposada wrote:Need some help understanding this one:

The value of (10^8 - 10^2)/(10^7 - 10^3) is closest to which of the following?

a - 1
b - 10
c - 10^2
d - 10^3
e - 10^4

the answer is b

Here's an alternate approach.

Whenever you see things being added or subtracted, ask yourself:

What is the GCF (the greatest common factor) that can be factored out of each term?

10^2 is the GCF of 10^8 and 10^2:
10^8 - 10^2
= 10^2(10^6 - 1)
= 10^2(10^6) approximately
= 10^8 approximately

10^3 is the GCF of 10^7 and 10^3:
10^7 - 10^3
= 10^3(10^4 - 1)
= 10^3(10^4) approximately
= 10^7 approximately

So (10^8 - 10^2)/(10^7 - 10^3)
= 10^8/10^7 approximately
= 10 approximately

The correct answer is B.

Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Like this post

pradeepkaushal9518: Legendary Member; Posts: 1309; Joined: Wed Mar 17, 2010 11:41 pmFollowed by: 5 members; Thanked: 33 times

by pradeepkaushal9518 » Mon Aug 02, 2010 2:10 am

really we have great instructors and experts. thanks to BTG

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 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