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by shashank.ism » Tue Feb 09, 2010 7:22 am
Given that f(0) = 0, f(1) = 1 and f(2) = 1. If f(n) = f(n+1) - f(n-1), then find the value of

(f(8) - f(7) + f(5))/(f(7) - f(6) - f(4)).

13/5
9/2
16/5
16/7
13/2
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by ajith » Tue Feb 09, 2010 9:52 am
shashank.ism wrote:Given that f(0) = 0, f(1) = 1 and f(2) = 1. If f(n) = f(n+1) - f(n-1), then find the value of

(f(8) - f(7) + f(5))/(f(7) - f(6) - f(4)).

13/5
9/2
16/5
16/7
13/2
f(3) = 1+1 = 2
f(4) = 2+1 = 3
f(5) = 2+3 = 5
f(6) = 3+5 =8
f(7) = 8+5 =13
f(8) = 13+8 = 21
(21 -13 + 5)/(13 - 8 - 3)
= 13/2
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by shashank.ism » Tue Feb 09, 2010 10:47 am
ajith wrote:
shashank.ism wrote:Given that f(0) = 0, f(1) = 1 and f(2) = 1. If f(n) = f(n+1) - f(n-1), then find the value of

(f(8) - f(7) + f(5))/(f(7) - f(6) - f(4)).

13/5
9/2
16/5
16/7
13/2
f(3) = 1+1 = 2
f(4) = 2+1 = 3
f(5) = 2+3 = 5
f(6) = 3+5 =8
f(7) = 8+5 =13
f(8) = 13+8 = 21
(21 -13 + 5)/(13 - 8 - 3)
= 13/2
ok so from f(n) = f(n+1) - f(n-1),
u rearranged to f(n+1) = f(n) + f(n-1)... good approach
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by thephoenix » Tue Feb 09, 2010 10:58 am
easiest way is to find out value for f3,f4,f5,f6,f7 ,f8and plug to get ans
f2=f3-f1-->f3=f2+f1---->f3=1+1=2
f3=f4-f2--->f4=f3+f2---->f4=2+1=3
f4=f5-f3--->f5=f4+f3---->f5=3+2=5
f5=f6-f4--->f6=f5+f4---->f6=5+3=8
f6=f7-f5---->f7=f6+f5--->f7=8+5=13
f7=f8-f6--->f8=f7+f6---->f7=13+8=21
now f8-f7+f5=21-13+5=13
f7-f6-f4=13-8-3=2
hence 13/2
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by harsh.champ » Tue Feb 09, 2010 1:16 pm
shashank.ism wrote:Given that f(0) = 0, f(1) = 1 and f(2) = 1. If f(n) = f(n+1) - f(n-1), then find the value of

(f(8) - f(7) + f(5))/(f(7) - f(6) - f(4)).

13/5
9/2
16/5
16/7
13/2
Its quite simple,
f(n+1) = f(n) + f(n-1)

Hence,f(3) = 2
f(4) = 3
f(5) = 5
f(6) = 8
f(7) = 13
f(8) = 21

Hence,(f(8) - f(7) + f(5))/(f(7) - f(6) - f(4)) = [21 - 13 + 5]/[13 - 8 - 3] [spoiler]= 13/2 which is E.[/spoiler]
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