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shikh: Senior | Next Rank: 100 Posts; Posts: 48; Joined: Sun Jul 17, 2011 12:04 am

by shikh » Sat Dec 03, 2011 2:01 am

S is an infinite sequence, in which the value of a particular member of the sequence is equal to the difference between the two preceding members of the sequence. What is the value of the 43rd member of the sequence?

(1) The 1st term is 1.
(2) The 3rd term is 3.

OA after discussion

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Source: Beat The GMAT — Data Sufficiency | Sat Dec 03, 2011 2:01 am

sam2304: Legendary Member; Posts: 1239; Joined: Tue Apr 26, 2011 6:25 amFollowed by: 26 members; Thanked: 233 times; GMAT Score:680

by sam2304 » Sat Dec 03, 2011 3:58 am

is the answer A ?

Initially i solved the question using both the statements but it seems we can solve it with A alone. The sequence repeats after 6 nos.

1.With 1st term as 1 the sequence repeats with every 6 nos. so 43rd term is equal to 1st term hence SUFF.

2nd term as 2 : 1 2 1 -1 -2 -1 1 2 1 -1 -2 -1 1
2nd term as 5 : 1 5 4 -1 -5 -4 1 5 4 -1 -5 -4 1

2.With the 3rd term as 3

2 5 3 -2 -5 -3 2
6 9 3 -6 -9 -3 6

Even in this sequence it follows a pattern based on the first digit. So with 3rd digit given we cannot find the answer and with 1st digit we can find it.

IMO A.

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kanwar86: Senior | Next Rank: 100 Posts; Posts: 99; Joined: Thu Jun 09, 2011 2:09 pm; Thanked: 11 times

by kanwar86 » Sat Dec 03, 2011 4:13 am

shikh wrote:S is an infinite sequence, in which the value of a particular member of the sequence is equal to the difference between the two preceding members of the sequence. What is the value of the 43rd member of the sequence?

(1) The 1st term is 1.
(2) The 3rd term is 3.

OA after discussion

IMO, C is the correct answer.

Regards

Kanwar

"In case my post helped, do care to thank. Happy learning

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shikh: Senior | Next Rank: 100 Posts; Posts: 48; Joined: Sun Jul 17, 2011 12:04 am

by shikh » Sat Dec 03, 2011 4:44 am

OA is A

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kanwar86: Senior | Next Rank: 100 Posts; Posts: 99; Joined: Thu Jun 09, 2011 2:09 pm; Thanked: 11 times

by kanwar86 » Sat Dec 03, 2011 5:41 am

kanwar86 wrote:
shikh wrote:S is an infinite sequence, in which the value of a particular member of the sequence is equal to the difference between the two preceding members of the sequence. What is the value of the 43rd member of the sequence?

(1) The 1st term is 1.
(2) The 3rd term is 3.

OA after discussion
IMO, C is the correct answer.

Agree...silly mistake...answer is A)

Regards

Kanwar

"In case my post helped, do care to thank. Happy learning

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