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# Suppose a1, a2, a3, ... is a sequence of integers such that a_n + 1 =

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Math Expert
Joined: 02 Sep 2009
Posts: 52296
Suppose a1, a2, a3, ... is a sequence of integers such that a_n + 1 =  [#permalink]

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28 Mar 2018, 23:18
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Difficulty:

15% (low)

Question Stats:

86% (01:12) correct 14% (01:07) wrong based on 52 sessions

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Suppose $$a_1$$, $$a_2$$, $$a_3$$, ... is a sequence of integers such that $$a_{n + 1} = 10a_n$$ . How many times greater is $$a_8$$ than $$a_3$$?

(A) 10^4
(B) 10^5
(C) 10^6
(D) 10^9
(E) 8^10 - 3^10

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Joined: 07 Dec 2017
Posts: 868
Re: Suppose a1, a2, a3, ... is a sequence of integers such that a_n + 1 =  [#permalink]

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28 Mar 2018, 23:37
1
Bunuel wrote:
Suppose $$a_1$$, $$a_2$$, $$a_3$$, ... is a sequence of integers such that $$a_{n + 1} = 10a_n$$ . How many times greater is $$a_8$$ than $$a_3$$?

(A) 10^4
(B) 10^5
(C) 10^6
(D) 10^9
(E) 8^10 - 3^10

If we're not familiar with the rules of arithmetic and geometric series, we can instead pick easy numbers.
This is an Alternative approach.

Since we're not given any exact numbers, why not pick the easiest possible number to use for calculation?
Say a3 = 1.
Then a4 = 10, a5 = 100, a6 = 1000, a7 = 10,000 and a8 = 100,000

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Re: Suppose a1, a2, a3, ... is a sequence of integers such that a_n + 1 = &nbs [#permalink] 28 Mar 2018, 23:37
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