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dtweah: Master | Next Rank: 500 Posts; Posts: 487; Joined: Fri Mar 27, 2009 5:49 am; Thanked: 36 times

by dtweah » Thu May 28, 2009 5:09 am

If in a sequence T1 = 2, T2 = 5, T3 = 11, T4 = 23, T5 = 47, What is T7?

A. 95

B. 96

C. 173

D. 181

E. 191

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Source: Beat The GMAT — Problem Solving | Thu May 28, 2009 5:09 am

sacx: Master | Next Rank: 500 Posts; Posts: 139; Joined: Wed Oct 22, 2008 4:36 am; Thanked: 17 times

by sacx » Thu May 28, 2009 5:24 am

T2-T1 = 3
T3-T2 = 6
T4-T3 = 12
T5-T4 = 24
T6 - T5 = 48, T6 = 95
T7-T6 = 96, T7 = 191

SACX

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abhinav85: Master | Next Rank: 500 Posts; Posts: 179; Joined: Mon Dec 29, 2008 4:41 am; Thanked: 2 times

by abhinav85 » Thu May 28, 2009 5:48 am

IMO E

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scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Thu May 28, 2009 10:34 am

by observation each term is 2 times the previous+1

T6: 2*47+1=95
T7: 2*95+1=191

hence, E

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ghacker: Master | Next Rank: 500 Posts; Posts: 148; Joined: Wed Jun 03, 2009 8:04 pmFollowed by: 1 member; Thanked: 18 times

by ghacker » Wed Jun 10, 2009 10:14 am

The answer is =4*47+3 = 191

or 47+144 = 191 ( the pattern is 3,6,12,24 so no )

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ketkoag: Legendary Member; Posts: 876; Joined: Thu Apr 10, 2008 8:14 am; Thanked: 13 times

by ketkoag » Thu Jun 11, 2009 4:56 am

pattern is Tn = 2*T(n-1) + 1
hence E would be the answer.

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