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# If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of

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If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of  [#permalink]

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13 Feb 2017, 03:21
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84% (01:41) correct 16% (01:36) wrong based on 80 sessions

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If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of f(3)?

A. -1
B. 3
C. 7
D. 11
E. 13

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Re: If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of  [#permalink]

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13 Feb 2017, 04:50
as i get, next term = previous term + 1
f(7+1)=f(7)+1 => f(8) = 4... f(6+1)=F(6)+1 so 3=f(6)+1=> f(6) = 2
so f(5)= 1 ; f(4)=0 and f(3) = -1

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Re: If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of  [#permalink]

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13 Feb 2017, 05:53
f(6) = 2... similarly f(3) is -1
ans A
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Re: If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of  [#permalink]

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14 Feb 2017, 16:52
2
Bunuel wrote:
If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of f(3)?

A. -1
B. 3
C. 7
D. 11
E. 13

We are given that f(x+1) = f(x) + 1 for all values of x and that f(7) = 3. We will be working “backward” to determine the value of f(3).

Let x = 6; then f(6+1) = f(6) + 1, i.e., f(7) = f(6) + 1.

Since f(7) = 3, we have 3 = f(6) + 1, i.e., f(6) = 2.

Let x = 5; then f(5+1) = f(5) + 1, i.e., f(6) = f(5) + 1.

Since f(6) = 2, we have 2 = f(5) + 1, i.e., f(5) = 1.

Let x = 4; then f(4+1) = f(4) + 1, i.e., f(5) = f(4) + 1.

Since f(5) = 1, we have 1 = f(4) + 1, i.e., f(4) = 0.

Let x = 3; then f(3+1) = f(3) + 1, i.e., f(4) = f(3) + 1.

Since f(4) = 0, we have 0 = f(3) + 1, i.e., f(3) = -1.

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Re: If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of  [#permalink]

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20 Feb 2017, 18:06
Um this one is kind of tripping me out but I'd say- If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of f(3)?- then the answer that follows is "A."
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Posts: 6960
Re: If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of  [#permalink]

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20 Feb 2017, 18:54
1
Bunuel wrote:
If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of f(3)?

A. -1
B. 3
C. 7
D. 11
E. 13

Hi...
A simpler way is to look at the choices..

Each term is ONE more than the previous term... F(x+1)=F(x)+1...

So if F(7) =3, F(3) has to be lesser than 3..
Only A is less than 3..

If you want to find exact answer, again no need to get into finding each term..
Difference in 7th and 3rd term is 4, so F(3) = F(7)-4=3-4=-1

A
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Re: If f(x+1)=f(x)+1 for all values of x, and f(7)=3, what is the value of &nbs [#permalink] 20 Feb 2017, 18:54
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