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Re: f(n) = f(n – 1) – n [#permalink]
17 Dec 2012, 23:46

1

This post received KUDOS

The equation says f(n) = f(n-1) - n (1) states f(3)=14 and we need to find f(4) so as per the equation, f(4) = f(4-1) -4 ==> f(4)=f(3)-4 ==> f(4)=14-4=10 So (1) is sufficient...Hope explanation for (2) is already clear. And this expalins the use of f(3)=14 as well. So the answer is D _________________

I don't understand what you mean slot straights into above equation. When I simplify the f(3) I get -1 and for f(6) I also get -1. Is that why both are sufficient? I don't understand why Statement 1 the f(3)=14. What I supposed to do something else?

I don't understand what you mean slot straights into above equation. When I simplify the f(3) I get -1 and for f(6) I also get -1. Is that why both are sufficient? I don't understand why Statement 1 the f(3)=14. What I supposed to do something else?

Hii. See the question gives us the relation: f(n)=f(n-1)-n and the question asks the value of f(4).

As per the above relation, if we expand f(4), we get: f(4)=f(3)-4---------[a]

Now coming to the statements: Statement 1 gives us direct f(3). We just have to put in equation [a]. Statement 2 gives us f(6)=-1. f(6) can be expanded as f(5)-6. Moreover f(5) can be expanded as f(4)-5. Put this value of f(5) in the former one. It will become f(6)=f(4)-9, which will gives the value of f(4) as 10.

Both are sufficient. Hope that helps. _________________

I don't understand what you mean slot straights into above equation. When I simplify the f(3) I get -1 and for f(6) I also get -1. Is that why both are sufficient? I don't understand why Statement 1 the f(3)=14. What I supposed to do something else?

Hii. See the question gives us the relation: f(n)=f(n-1)-n and the question asks the value of f(4).

As per the above relation, if we expand f(4), we get: f(4)=f(3)-4---------[a]

Now coming to the statements: Statement 1 gives us direct f(3). We just have to put in equation [a]. Statement 2 gives us f(6)=-1. f(6) can be expanded as f(5)-6. Moreover f(5) can be expanded as f(4)-5. Put this value of f(5) in the former one. It will become f(6)=f(4)-9, which will gives the value of f(4) as 10.

Both are sufficient. Hope that helps.

Yes, thank you! But we don't use the =14 anywhere? What's the purpose of it then?

Re: If n is an integer and f(n) = f(n 1) n, what is the value of [#permalink]
17 Dec 2012, 23:41

Expert's post

In statement 1, put f(3)=14. You will get the answer as 10. In DS, if you know that with the given information a particular question can be solved then rather than trying to find the exact answer, move to the next statement. In the explanation, I did the same.

I don't understand what you mean slot straights into above equation. When I simplify the f(3) I get -1 and for f(6) I also get -1. Is that why both are sufficient? I don't understand why Statement 1 the f(3)=14. What I supposed to do something else?

Re: If n is an integer and f(n) = f(n 1) n, what is the value of [#permalink]
31 Jan 2014, 09:49

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