GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 18 Dec 2018, 03:00

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

## Events & Promotions

###### Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Happy Christmas 20% Sale! Math Revolution All-In-One Products!

December 20, 2018

December 20, 2018

10:00 PM PST

11:00 PM PST

This is the most inexpensive and attractive price in the market. Get the course now!
• ### Key Strategies to Master GMAT SC

December 22, 2018

December 22, 2018

07:00 AM PST

09:00 AM PST

Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.

# For which of the following functions f(x) is f(a + b) = f(a) ?

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 51281
For which of the following functions f(x) is f(a + b) = f(a) ?  [#permalink]

### Show Tags

30 Jul 2018, 23:31
00:00

Difficulty:

(N/A)

Question Stats:

84% (00:58) correct 16% (01:06) wrong based on 55 sessions

### HideShow timer Statistics

For which of the following functions f(x) is $$f(a + b) = f(a) + f(b)$$?

(A) $$f(x) = x^2$$

(B) $$f(x) = 5x$$

(C) $$f(x) = 2x + 1$$

(D) $$f(x) =\sqrt{x}$$

(E) $$f(x) = x - 2$$

_________________
examPAL Representative
Joined: 07 Dec 2017
Posts: 842
Re: For which of the following functions f(x) is f(a + b) = f(a) ?  [#permalink]

### Show Tags

31 Jul 2018, 00:32
Bunuel wrote:
For which of the following functions f(x) is $$f(a + b) = f(a) + f(b)$$?

(A) $$f(x) = x^2$$

(B) $$f(x) = 5x$$

(C) $$f(x) = 2x + 1$$

(D) $$f(x) =\sqrt{x}$$

(E) $$f(x) = x - 2$$

Instead of trying to work with the equations, we'll pick easy numbers to eliminate incorrect answers.
This is an Alternative approach.

Say a = 1 and b = 1, so a+b = 2.
Then (A) gives f(2) = 4 but f(1) + f(1) = 2. NO!
(B) gives f(2) = 10 and f(1)+f(1) = 10. Maybe let's check the others.
(C) gives f(2) = 5 but f(1) + f(1) = 6. NO!
(D) gives f(2) = $$\sqrt{2}$$ while f(1)+f(1) = 2. NO
(E) gives f(2) = 0 and f(1) + f(1) = -2. NO

_________________

Happy holidays!

Intern
Joined: 09 Jul 2018
Posts: 9
Re: For which of the following functions f(x) is f(a + b) = f(a) ?  [#permalink]

### Show Tags

31 Jul 2018, 16:43
I did not really understand what the question is asking, can someone explain the question?
Math Expert
Joined: 02 Sep 2009
Posts: 51281
Re: For which of the following functions f(x) is f(a + b) = f(a) ?  [#permalink]

### Show Tags

31 Jul 2018, 23:50
1
Sandy56 wrote:
I did not really understand what the question is asking, can someone explain the question?

I explained very similar question in detail HERE.

Also, check below topics:

13. Functions

For more check below:
ALL YOU NEED FOR QUANT ! ! !

Hope it helps.
_________________
Senior Manager
Joined: 17 Mar 2014
Posts: 375
For which of the following functions f(x) is f(a + b) = f(a) ?  [#permalink]

### Show Tags

Updated on: 01 Aug 2018, 19:50
2
Sandy56 wrote:
I did not really understand what the question is asking, can someone explain the question?

Question asks which of below functions can behave like$$f(a+b)=f(a)+f(b)$$.

Now what does$$f(a+b)$$ mean ? It can be any function. when we reading question stem we don't know its value. We need to find out of available options.

Now what does$$f(a+b)=f(a)+f(b)$$ mean ? it means, for example, f(5)=5 and f(6)=6 then f(5+6)= 5+6= f(5)+(6).

Now check available options one by one.

(A)$$f(x)=x^2$$ => $$f(a)=a^2$$ , $$f(b)=b^2$$ and $$f(a+b)=(a+b)^2$$$$= a^2+2ab+b^2$$ which is not equal to $$f(a)+(b)$$

(B)$$f(x)=5x$$ =>$$f(a)=5a$$, $$f(b)=5b$$ and $$f(a+b)=5(a+b)= 5a+5b= f(a) +f(b)$$ Whoohoo..here you go. This is the answer

(C) $$f(x)=2x+1$$

(D)$$f(x)=\sqrt{x}$$

(E) $$f(x)=x−2$$

Pls find similar question to practice: https://gmatclub.com/forum/for-which-of ... 24491.html

Originally posted by ammuseeru on 01 Aug 2018, 19:38.
Last edited by ammuseeru on 01 Aug 2018, 19:50, edited 1 time in total.
Senior Manager
Joined: 17 Mar 2014
Posts: 375
For which of the following functions f(x) is f(a + b) = f(a) ?  [#permalink]

### Show Tags

01 Aug 2018, 19:41
DavidTutorexamPAL wrote:
Bunuel wrote:
For which of the following functions f(x) is $$f(a + b) = f(a) + f(b)$$?

(A) $$f(x) = x^2$$

(B) $$f(x) = 5x$$

(C) $$f(x) = 2x + 1$$

(D) $$f(x) =\sqrt{x}$$

(E) $$f(x) = x - 2$$

Instead of trying to work with the equations, we'll pick easy numbers to eliminate incorrect answers.
This is an Alternative approach.

Say a = 1 and b = 1, so a+b = 2.
Then (A) gives f(2) = 4 but f(1) + f(1) = 2. NO!
(B) gives f(2) = 10 and f(1)+f(1) = 10. Maybe let's check the others.
(C) gives f(2) = 5 but f(1) + f(1) = 6. NO!
(D) gives f(2) = $$\sqrt{2}$$ while f(1)+f(1) = 2. NO
(E) gives f(2) = 0 and f(1) + f(1) = -2. NO

In my opinion, it is very basic fundamental question. I don't know whether we really need number to put in and check. If student's basic math fundamentals are clear, Student should be able to solve it visually.
For which of the following functions f(x) is f(a + b) = f(a) ? &nbs [#permalink] 01 Aug 2018, 19:41
Display posts from previous: Sort by