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Sequence Problem

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Sequence Problem

by ILULA08 » Tue Jul 28, 2009 11:04 pm
If sequence a1, a2.........an is such that an= 2(an-1) -x for all
positive integers n>=2 and for certain number x. If a5= 99 and
a3=27, what is the value of x?

a)3
b)9
c)18
d)36
e)42
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by Robinmrtha » Tue Jul 28, 2009 11:36 pm
we have
an= 2(an-1) -x

we have
a5= 99
or an= 2(an-1) -x
or 99=2a4-x---------------eqn 1

a3=27
or an= 2(an-1) -x
or a4=2a3-x
or a4=54-x

substitute this value is eqn 1
we get x = 3

Ans is A
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Senior | Next Rank: 100 Posts
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by ILULA08 » Wed Jul 29, 2009 4:06 am
Thanks a lot. I dont know how I missed it :)
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