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If n is an integer and f(n) = f(n 1) n, what is the value of [#permalink]
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15 Jun 2011, 15:30
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If n is an integer and f(n) = f(n – 1) – n, what is the value of f (4)? (1) f(3) = 14 (2) f(6) = 1
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Re: f(n) = f(n – 1) – n [#permalink]
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15 Jun 2011, 16:16
f(4) = f(3)  4
1) Sufficient, slot straights into above equation.
2) f(6) = 1 = f(5)  6 f(5) = 5 = f(4)  5 f(4) = 10 Sufficient
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If n is an integer and f(n) = f(n – 1) – n, what is the [#permalink]
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02 Aug 2012, 15:58
If n is an integer and f(n) = f(n – 1) – n, what is the value of f (4)?
(1) f(3) = 14
(2) f(6) = 1
Last edited by Bunuel on 02 Aug 2012, 16:25, edited 1 time in total.
Moved to DS subforum and renamed the topic.



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Re: If n is an integer and f(n) = f(n – 1) – n, what is the [#permalink]
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02 Aug 2012, 16:30



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Re: f(n) = f(n – 1) – n [#permalink]
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17 Dec 2012, 21:55
pike wrote: f(4) = f(3)  4
1) Sufficient, slot straights into above equation.
2) f(6) = 1 = f(5)  6 f(5) = 5 = f(4)  5 f(4) = 10 Sufficient
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?



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Re: f(n) = f(n – 1) – n [#permalink]
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17 Dec 2012, 22:25
dcastan2 wrote: pike wrote: f(4) = f(3)  4
1) Sufficient, slot straights into above equation.
2) f(6) = 1 = f(5)  6 f(5) = 5 = f(4)  5 f(4) = 10 Sufficient
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?Hii. See the question gives us the relation: \(f(n)=f(n1)n\) 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.
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Re: f(n) = f(n – 1) – n [#permalink]
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18 Dec 2012, 00:14
Marcab wrote: dcastan2 wrote: pike wrote: f(4) = f(3)  4
1) Sufficient, slot straights into above equation.
2) f(6) = 1 = f(5)  6 f(5) = 5 = f(4)  5 f(4) = 10 Sufficient
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?Hii. See the question gives us the relation: \(f(n)=f(n1)n\) 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?



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Re: If n is an integer and f(n) = f(n 1) n, what is the value of [#permalink]
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18 Dec 2012, 00:41
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. Hope that helps.
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Re: f(n) = f(n – 1) – n [#permalink]
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18 Dec 2012, 00:46
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The equation says f(n) = f(n1)  n (1) states f(3)=14 and we need to find f(4) so as per the equation, f(4) = f(41) 4 ==> f(4)=f(3)4 ==> f(4)=144=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
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