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Math Revolution GMAT Instructor
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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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Re: The terms of the sequence {An} satisfy A2 - A1 = 2, A3 - A2 = 5 and A4 [#permalink]
Expert Reply
=>

We try each possibility until we find a formula that works.
A): If An+1 - An = n + 1, then A2 - A1 = \(1 + 1 = 2\), which is correct, but
A3 - A2 = \(2 + 1 = 3 ≠ 5.\)
So, A) is not the answer.
B): If An+1 - An = \(n^2 +\)1, then
A2 - A1 = \(1^2 + 1 = 2,\)
A3 - A2 =\(2^2 + 1 = 5,\)
A4 - A3 = \(3^2 + 1 = 10.\)
So, this formula is possible.

Therefore, the answer is B.
Answer: B
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Re: The terms of the sequence {An} satisfy A2 - A1 = 2, A3 - A2 = 5 and A4 [#permalink]
A2-A1=2, A3-A2=5
using options for answer
putting n=2 difference is 5
A.n+1
2+1=3 incorrect
B.n^2+1
2^2+1=5(can be a answer)
C.n^2−1
2^2-1=3
Incorrect
D.n−1
2-1=1 incorrect
E.n^2+3
2^2+3=7 incorrect

So answer is B
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Re: The terms of the sequence {An} satisfy A2 - A1 = 2, A3 - A2 = 5 and A4 [#permalink]
MathRevolution wrote:
=>

We try each possibility until we find a formula that works.
A): If An+1 - An = n + 1, then A2 - A1 = \(1 + 1 = 2\), which is correct, but
A3 - A2 = \(2 + 1 = 3 ≠ 5.\)
So, A) is not the answer.
B): If An+1 - An = \(n^2 +\)1, then
A2 - A1 = \(1^2 + 1 = 2,\)
A3 - A2 =\(2^2 + 1 = 5,\)
A4 - A3 = \(3^2 + 1 = 10.\)
So, this formula is possible.

Therefore, the answer is B.
Answer: B


Hi Math Revolution good question could you list some similar questions ?

Bunuel if you would know some similar sums will really help!
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Re: The terms of the sequence {An} satisfy A2 - A1 = 2, A3 - A2 = 5 and A4 [#permalink]
Expert Reply
Sri07 wrote:
MathRevolution wrote:
=>

We try each possibility until we find a formula that works.
A): If An+1 - An = n + 1, then A2 - A1 = \(1 + 1 = 2\), which is correct, but
A3 - A2 = \(2 + 1 = 3 ≠ 5.\)
So, A) is not the answer.
B): If An+1 - An = \(n^2 +\)1, then
A2 - A1 = \(1^2 + 1 = 2,\)
A3 - A2 =\(2^2 + 1 = 5,\)
A4 - A3 = \(3^2 + 1 = 10.\)
So, this formula is possible.

Therefore, the answer is B.
Answer: B


Hi Math Revolution good question could you list some similar questions ?

Bunuel if you would know some similar sums will really help!




12. Sequences



For other subjects:
ALL YOU NEED FOR QUANT ! ! !
Ultimate GMAT Quantitative Megathread

Hope it helps.
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Re: The terms of the sequence {An} satisfy A2 - A1 = 2, A3 - A2 = 5 and A4 [#permalink]
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Re: The terms of the sequence {An} satisfy A2 - A1 = 2, A3 - A2 = 5 and A4 [#permalink]
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