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# sequence

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Intern
Joined: 02 Jun 2009
Posts: 21

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02 Jun 2009, 03:44
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The sequence A1, A2, ......., An, ..... is such that An = 2An-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) 45
Intern
Joined: 12 May 2009
Posts: 46
Location: Mumbai

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02 Jun 2009, 04:06
Given: An = 2A(n-1) - x

A5 = 2A4 - x
A4 = 2A3 - x
Given--> A3 = 27
=> A4 = 2*27 - x = 54-x
=> A5 = 2(54-x) - x
Also given --> A5 = 99
=> 99 = 108 - 3x
=> x=3

IMO A
Re: sequence   [#permalink] 02 Jun 2009, 04:06
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# sequence

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