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# Sequence

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Manager
Joined: 16 Apr 2009
Posts: 230
Schools: Ross

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03 Jun 2009, 17:42
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A sequence, a1=64, a2=66, a3=67, an=8+an-3, which of the following is in the sequence?

105
786
966
1025
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SVP
Joined: 29 Aug 2007
Posts: 2467

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03 Jun 2009, 18:13
1
KUDOS
vannu wrote:
A sequence, a1=64, a2=66, a3=67, an=8+an-3, which of the following is in the sequence?

105
786
966
1025

Thats a good question but AC (answer choice) E is missing.

a1 = 64
a2 = 66
a3 = 67

an = 8 + a(n-3)
a3 = 8 + a0
a0 = 67-8 = 59

a4 = a1 + 8 = 64 + 8 = 72
a5 = a2 + 8 = 66 + 8 = 74
a6 = a3 + 8 = 67 + 8 = 75

A. (105 - 64)/8 = k where k must be an integer but k is not.
(105 - 66)/8 = m where m must be an integer but m is not.
(105 - 67)/8 = n where n must be an integer but n is not.
So A is not

B. (786 - 64)/8 = x where x must be an integer but x is not.
(786 - 66)/8 = 720/8 = 90 = y where y must be an integer and y is an integer. Bingo....
(786 - 67)/8 = z where z must be an integer but z is not.
B is.

C. (966 - 64)/8 = p where p must be an integer but p is not.
(966 - 66)/8 = q where q must be an integer but q is not.
(966 - 67)/8 = r where r must be an integer but r is not.

C is not.
D. (1025 - 64)/8 = a where a must be an integer but a is not.
(1025 - 66)/8 = b where b must be an integer but b is not.
(1025 - 67)/8 = c where c must be an integer but c is not.

D is not.

Therefore it is B.
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Senior Manager
Joined: 15 Jan 2008
Posts: 275

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04 Jun 2009, 00:58
MY logic of approach..

All the numbers in this sequence will remainder 0,2,3 when divided by 8.

So if the remainder is one of the above, its in the sequence..

B gives teh remaider 2.. and hence in the sequence.
Intern
Joined: 12 May 2009
Posts: 46
Location: Mumbai

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04 Jun 2009, 04:00
IMO B

I took 8 as base and i got the 0, 2, 3 as reminder.
Dividing the numbers i got only 786 as match which had reminder 2.
Senior Manager
Joined: 16 Jan 2009
Posts: 355
Concentration: Technology, Marketing
GMAT 1: 700 Q50 V34
GPA: 3
WE: Sales (Telecommunications)

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04 Jun 2009, 11:37
IMO B.

we can devide each option by 8 to find from which (a1 / a2 / a3) it as been derived.
The range of remainders is 0 / 2 /3
786 has reminder 2.
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Re: Sequence   [#permalink] 04 Jun 2009, 11:37
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