(3^9 - 3^8) (3^7 - 3^6) =
(A) 3^4
(B) 3^14
(C) 6^14
(D) 2 × 3^14
(E) 4 × 3^14
[spoiler]Source: https://readyforgmat.com[/spoiler]
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
(3^9 – 3^8) (3^7 – 3^6) =
This topic has expert replies
-
sanju09
- GMAT Instructor
- Posts: 3650
- Joined: Wed Jan 21, 2009 4:27 am
- Location: India
- Thanked: 267 times
- Followed by:80 members
- GMAT Score:760
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
GMAT/MBA Expert
-
Rahul@gurome
- GMAT Instructor
- Posts: 1179
- Joined: Sun Apr 11, 2010 9:07 pm
- Location: Milpitas, CA
- Thanked: 447 times
- Followed by:88 members
(3^9 - 3^8) (3^7 - 3^6) = 3^8 (3 - 1) * 3^6(3 - 1) = 3^14 * 4
The correct answer is [spoiler](E)[/spoiler].
The correct answer is [spoiler](E)[/spoiler].
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
-
Brian@VeritasPrep
- GMAT Instructor
- Posts: 1031
- Joined: Thu Jul 03, 2008 1:23 pm
- Location: Malibu, CA
- Thanked: 716 times
- Followed by:255 members
- GMAT Score:750
Hey everyone:
Rahul is dead on, but just in reading the subject line here I was reminded of a point I've made on here a lot lately. With exponents all of the rules that we know are related to multiplication/division and not addition/subtraction. It's tempting to want to just add or subtract here, but we don't have any rules that will help us do so with such large numbers.
When you see addition/subtraction in exponential problems, you'll almost always have to:
1) Factor to set up multiplication
2) Use the exponent rules for multiplication of same bases
3) Simplify, answer correctly, score 750, enroll at Stanford GSB
(3rd step optional, but recommended)
Rahul is dead on, but just in reading the subject line here I was reminded of a point I've made on here a lot lately. With exponents all of the rules that we know are related to multiplication/division and not addition/subtraction. It's tempting to want to just add or subtract here, but we don't have any rules that will help us do so with such large numbers.
When you see addition/subtraction in exponential problems, you'll almost always have to:
1) Factor to set up multiplication
2) Use the exponent rules for multiplication of same bases
3) Simplify, answer correctly, score 750, enroll at Stanford GSB
(3rd step optional, but recommended)
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.
GMAT Instructor
Chief Academic Officer
Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.
-
Chirawat Sungkamee
- Newbie | Next Rank: 10 Posts
- Posts: 2
- Joined: Sun Aug 19, 2012 11:28 pm
SOLUTION IN DETAIL:
Due to x^a * x^b = x^a+b, therefore
(3^9 - 3^8)(3^7 - 3^6) = (3^8 * 3^1 - 3^8)(3^6 * 3^1 - 3^6)
= (3^8 * 3 - 3^8)(3^6 * 3 - 3^6)
= {3^8(3-1)}{3^6(3-1)}
= 3^8 * 2 * 3^6 * 2
= 2 * 2 * 3^8 * 3^6
= 4 * 3^8+6
= 4 * 3^14
The answer is (E).
Due to x^a * x^b = x^a+b, therefore
(3^9 - 3^8)(3^7 - 3^6) = (3^8 * 3^1 - 3^8)(3^6 * 3^1 - 3^6)
= (3^8 * 3 - 3^8)(3^6 * 3 - 3^6)
= {3^8(3-1)}{3^6(3-1)}
= 3^8 * 2 * 3^6 * 2
= 2 * 2 * 3^8 * 3^6
= 4 * 3^8+6
= 4 * 3^14
The answer is (E).
