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# If the sequence a1, a2, a3, ..., an is such that a1 = 6 and an = 2a

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Math Expert
Joined: 02 Sep 2009
Posts: 54376
If the sequence a1, a2, a3, ..., an is such that a1 = 6 and an = 2a  [#permalink]

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03 Apr 2019, 23:16
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Difficulty:

25% (medium)

Question Stats:

79% (01:23) correct 21% (01:19) wrong based on 14 sessions

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If the sequence $$a_1$$,$$a_2$$, $$a_3$$, ..., $$a_n$$ is such that $$a_1 = 6$$ and $$a_n = 2a_{(n - 1)}$$ for $$n > 1$$, then $$a_6 - a_5 =$$

A. 12

B. 48

C. 64

D. 96

E. 192

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Re: If the sequence a1, a2, a3, ..., an is such that a1 = 6 and an = 2a  [#permalink]

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04 Apr 2019, 02:17
Bunuel wrote:
If the sequence $$a_1$$,$$a_2$$, $$a_3$$, ..., $$a_n$$ is such that $$a_1 = 6$$ and $$a_n = 2a_{(n - 1)}$$ for $$n > 1$$, then $$a_6 - a_5 =$$

A. 12

B. 48

C. 64

D. 96

E. 192

a1=6
a2=12
a3=24
a4=48
a5=96
a6==192
192-96 = 96
IMO D
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Re: If the sequence a1, a2, a3, ..., an is such that a1 = 6 and an = 2a  [#permalink]

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09 Apr 2019, 23:27
an=2a(n−1) therefore a6 = 2 X a5

we will put this value in the given equation,

a6- a5 = 2 x a5 - a5 = a5

therefore ans is D.
Re: If the sequence a1, a2, a3, ..., an is such that a1 = 6 and an = 2a   [#permalink] 09 Apr 2019, 23:27
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# If the sequence a1, a2, a3, ..., an is such that a1 = 6 and an = 2a

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