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

Redeem

Question from GMAT prep

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 210
Joined: Thu Mar 08, 2012 11:24 pm
Thanked: 62 times
Followed by:3 members

by niketdoshi123 » Fri Apr 13, 2012 10:53 pm
alex.gellatly wrote:For which of the following functions is f(a + b) = f(a) + f(b)for all positive numbers a and b ?
(A) f(x) = x2
(B) f(x) = x+1
(C) f(x) = x
(D) f(x) = (2) / (x)
(E) f(x) = -3x
assuming a=3 and b=5

a) f(x)=x2
f(a+b)= f(3+5)=64
f(a)+f(b)= f(3)+f(5)= 34

b)f(x) = x+1
f(a+b) = f(3+5)= 9
f(a)+f(b)= f(3)+f(5)=(3+1)+(5+1)=10

c)f(x)=x
f(a+b)=f(3+5)=8
f(a)+f(b)=3+5=8

d)f(x)=2/x
f(a+b)=f(3+5)=2/8=1/4
f(a)+f(b)=f(3)+f(5)= (2/3) + (2/5)=16/15

e)f(x)=-3x
f(a+b)=f(3+5)=-24
f(a)+f(b)=f(3)+f(5)= -9-15= -24

both [spoiler]c & e[/spoiler] satisfy the function
Top
User avatar
Legendary Member
Posts: 1239
Joined: Tue Apr 26, 2011 6:25 am
Thanked: 233 times
Followed by:26 members
GMAT Score:680

by sam2304 » Fri Apr 13, 2012 11:29 pm
alex.gellatly wrote:For which of the following functions is f(a + b) = f(a) + f(b)for all positive numbers a and b ?
(A) f(x) = x2
(B) f(x) = x+1
(C) f(x) = x
(D) f(x) = (2) / (x)
(E) f(x) = -3x
Is the question proper ? ? Two right answers are there.
Getting defeated is just a temporary notion, giving it up is what makes it permanent.
https://gmatandbeyond.blogspot.in/
Top
Legendary Member
Posts: 581
Joined: Sun Apr 03, 2011 7:53 am
Thanked: 52 times
Followed by:5 members

by killer1387 » Fri Apr 13, 2012 11:42 pm
For which of the following functions is f(a + b) = f(a) + f(b)for all positive numbers a and b ?
(A) f(x) = x2
(B) f(x) = x+1
(C) f(x) = x
(D) f(x) = (2) / (x)
(E) f(x) = -3x

BOTH C and E are good here (doubt if its a GMAT PREP problem)

because both presents option that is a straight line passing through origin and will satisfy the function given in the question.
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 » Sat Apr 14, 2012 5:08 am
I posted a solution here:

https://www.beatthegmat.com/gmat-prep-fu ... 67229.html

Answer choice C should read √x.
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
Master | Next Rank: 500 Posts
Posts: 435
Joined: Wed Nov 16, 2011 7:27 am
Thanked: 48 times
Followed by:16 members

by alex.gellatly » Sun Apr 15, 2012 12:51 am
Sorry everyone for typing the answer choices incorrectly!!!!!! and Thanks a lot for your help.
Top
Post new topic Post Reply
• Page 1 of 1