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Master | Next Rank: 500 Posts
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by Xbond » Thu Jun 11, 2009 1:12 pm
Hi there,

I don't understand anything to this PS. Could you explain the concept (simple way)?

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)= (root) x

d) f(x)= 2/x

e) f(x)= -3x
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by Claret » Thu Jun 11, 2009 1:47 pm
if you are stumped at questions with variables in answer choices, the golden rule is PLUG in for the variables

for the question above , say a =1 , b=1

substitute above values in the question stem :
f(2) = 2f(1)

now substitute the values of a and b in the answer choices and see which one satisfies f(2) = 2f(1)

only E does, hence it is the answer!

hope it helps..
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by gmatplayer » Thu Jun 11, 2009 1:47 pm
Replace x with addition of two numbers.
For example x = 4 + 3,
Then substitute a=4 and b=3

Do it for all options
(E) is the answer

f(x)= -3(x)
= -3(4+3)
= -21

And f(x) = -3(4) + (-3(3))
= -12 - 9
=-21
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Master | Next Rank: 500 Posts
Posts: 103
Joined: Fri May 22, 2009 3:56 am
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GMAT Score:470

by gmatplayer » Thu Jun 11, 2009 1:50 pm
Replace x with addition of two numbers.
For example x = 4 + 3,
Then substitute a=4 and b=3

Do it for all options
(E) is the answer

f(x)= -3(x)
= -3(4+3)
= -21

And f(x) = -3(4) + (-3(3))
= -12 - 9
=-21
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