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Number terms

by karthikpandian19 » Tue Nov 08, 2011 8:28 pm
If sequence S has 250 terms, what is the 243r term of S?

1. The 242nd term of S is -494
2.The first term of S is -12 and each term of S after the first term is 2 less than the preceding term

What is the answer and explanation?
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by user123321 » Tue Nov 08, 2011 8:37 pm
karthikpandian19 wrote:If sequence S has 250 terms, what is the 243r term of S?

1. The 242nd term of S is -494
2.The first term of S is -12 and each term of S after the first term is 2 less than the preceding term

What is the answer and explanation?
1) Since by just knowing a term, we cannot determine another term in a sequence, because we need to know the common difference. hence insufficient.
2) a = -12
d = -2
so 243rd term = -12+(243-1)*(-2)
hence sufficient.

[spoiler]is it B?[/spoiler]

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by karthikpandian19 » Tue Nov 08, 2011 8:42 pm
user123321 wrote:
karthikpandian19 wrote:If sequence S has 250 terms, what is the 243r term of S?

1. The 242nd term of S is -494
2.The first term of S is -12 and each term of S after the first term is 2 less than the preceding term

What is the answer and explanation?
1) Since by just knowing a term, we cannot determine another term in a sequence, because we need to know the common difference. hence insufficient.
2) a = -12
d = -2
so 243rd term = -12+(243-1)*(-2)
hence sufficient.

[spoiler]is it B?[/spoiler]

user123321
right answer is perfectly B
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by neelgandham » Wed Nov 09, 2011 2:41 am
If sequence S has 250 terms, what is the 243r term of S?

1. The 242nd term of S is -494.
If the sequence is a sequence of ascending numbers and if all the terms in the sequence are integers than 243rd term = -493

If the sequence is a sequence of ascending numbers and if all the terms in the sequence are integers than 243rd term = -495

One can get multiple answers/multiple sequence types.Hence, insufficient.
2.The first term of S is -12 and each term of S after the first term is 2 less than the preceding term
First term = -12, nth term = -12 - (2*(n-1)) when n = 243, nth term = 12 - (2*(243-1)). Sufficient
IMO B
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by bpdulog » Wed Nov 09, 2011 10:30 am
Looks like it's B.

[spoiler]1)[/spoiler] is forcing you to believe a certain pattern exists, when in fact there are many possibilities.
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