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

Redeem

Functions Question

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 10
Joined: Tue May 22, 2012 8:42 am
Followed by:1 members

Functions Question

by Tdot23 » Wed May 23, 2012 4:16 am
Hello Community,
I am having much trouble tackling PS questions with functions. If there is a one clear way about going at them please do share and thanks in advance for taking a look at my question from the GMAC test:

Q: If f(a+b) = f(a) + f(b) for all positive a and b what is f(a+b)?

[Sorry, this question was shortened when I quickly wrote it down after taking the test at an off-site so don't have the exact woring here but hopefully the idea translates...]

A:
(a) f(x) = x^2
(b) f(x) = x+1
(c) f(x) = Root x
(d) f(x) = 2/x
(e) f(x) = -3x

The correct answer is (e)... but I would really like to "understand" it.. Thanks again!
Top
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Wed May 23, 2012 4:26 am
NYC23 wrote:Hello Community,
I am having much trouble tackling PS questions with functions. If there is a one clear way about going at them please do share and thanks in advance for taking a look at my question from the GMAC test:

Q: If f(a+b) = f(a) + f(b) for all positive a and b what is f(a+b)?

[Sorry, this question was shortened when I quickly wrote it down after taking the test at an off-site so don't have the exact woring here but hopefully the idea translates...]

A:
(a) f(x) = x^2
(b) f(x) = x+1
(c) f(x) = Root x
(d) f(x) = 2/x
(e) f(x) = -3x

The correct answer is (e)... but I would really like to "understand" it.. Thanks again!
One method is as follows:


Let's analyze each of the options individually:

1. (a + b)² ≠ (a² + b²) => f(a + b) ≠ f(a) + f(b)
2. (a + b + 1) ≠ (a + 1) + (b + 1) = (a + b + 2) => f(a + b) ≠ f(a) + f(b)
3. √(a + b) ≠ (√a + √b) => f(a + b) ≠ f(a) + f(b)
4. 2/(a + b) ≠ (2/a) + (2/b) = 2(a + b)/ab => f(a + b) ≠ f(a) + f(b)
5. (-3(a + b)) = (-3a) + (-3b) => f(a + b) = f(a) + f(b)

The correct answer is E.
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/
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Wed May 23, 2012 4:31 am
I posted an alternate approach here:

https://www.beatthegmat.com/gmat-prep-fu ... 67229.html
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
Top
Post new topic Post Reply
• Page 1 of 1