Sequence of numbers {PS}

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dell2: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Thu Jun 02, 2011 10:28 am

by dell2 » Wed Jan 18, 2012 12:03 pm

A sequence of numbers is such that a1 = 11, a2 =16, and each subsequent an = an-2 + 9. Which of the following numbers is a member of the sequence?

A 216
B 246
C 289
D 299
E 368

OA : 299

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Source: Beat The GMAT — Problem Solving | Wed Jan 18, 2012 12:03 pm

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Wed Jan 18, 2012 12:18 pm

a(n) can be represented as either 11+9K (or) 16+9K

therefore a(n) - 11 (or) a(n) - 16 should be multiple of 9.

Only 299 - 11 = 288 is a multiple of 9 - D

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