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by resilient » Tue Feb 19, 2008 5:23 pm
If n is an integer, f(n) = f(n – 1) – n, and f(4) = 10. What is the value of f(6)?
a.-1
b.0
c.1
d.2
e.4


I am not following the chain of events here and need to figure this function out.
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qa

by resilient » Tue Feb 19, 2008 5:27 pm
Im getting thrown off by f(4) = 10

Can I just simply plug in 6 for N.

f(n)=f(n-1)-n
f(6)=f(6-1)-6 ===> f(6)=f 5-6 = -1


I am gettingthe right answer but am I on the right track here?








qa is A /-1
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by siddarthd2919 » Tue Feb 19, 2008 7:29 pm
the problem can be solved as follows:
f(4)= f(3)-4

10= f(3)-4

f(3) = 14.....similarly u will get f(2) =17......f(1)=19......f(0)=20

now these no follow a sequence

f() 20 19 17 14 10 ?
the difference 1 2 3 4 5


so f(5) = 5

so f(6) = 5-6 === -1 :)
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symblisms

by resilient » Wed Feb 20, 2008 12:35 am
this is very close to symbolism problems. thanks for the in depth answer. I appreciate it.. but I think I need some more pracitce in this department. lol
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by mba.dude » Wed Feb 20, 2008 6:53 am
One explanation can be :

F(4) = 10 (Given in question)

F(6) = F(5)- 6
and F(5) = F(4) - 5

So F(6) = F(4) - 5 -6 = F(4) - 11
F(6) = 10 - 11 = -1
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by Stuart@KaplanGMAT » Wed Feb 20, 2008 1:54 pm
siddarthd2919 wrote:the problem can be solved as follows:
f(4)= f(3)-4

10= f(3)-4

f(3) = 14.....similarly u will get f(2) =17......f(1)=19......f(0)=20

now these no follow a sequence

f() 20 19 17 14 10 ?
the difference 1 2 3 4 5


so f(5) = 5

so f(6) = 5-6 === -1 :)
This is the right idea, but by going down instead of up you really increased the amount of work.

This question is really a sequence question. We're given the defining rule:

f(n) = f(n-1) - n

and we know that f(4) = 10. Since we want f(6), we should work up in terms, not down.

First, let n=5

f(5) = f(4) - 5 = 10 - 5 = 5

then, let n=6

f(6) = f(5) - 6 = 5 - 6 = -1
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