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.
functions
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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
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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This is the right idea, but by going down instead of up you really increased the amount of work.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 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
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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