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DS sequence.

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DS sequence.

by rakeshd347 » Fri Oct 04, 2013 11:36 pm
Given a sequence: a1,a2,a3,a4......

In the sequence shown,an=(an-1)+k , where 2<=n<=15 and k is a nonzero constant. How many of the terms in the sequence are greater than 10?

(1) a1=24
(2) a8=10

OA coming soon.


Just to clarify
an= nth term of the sequence and
an-1= n-1th term of the sequence.
Last edited by rakeshd347 on Fri Oct 04, 2013 11:56 pm, edited 1 time in total.
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Source: — Data Sufficiency |
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by theCodeToGMAT » Fri Oct 04, 2013 11:48 pm
rakeshd347 wrote:Given a sequence: a1,a2,a3,a4......
In the sequence shown,an=(an-1)+k , where and k is a nonzero constant. How many of the terms in the sequence are greater than 10?

(1) a1=24
(2) a8=10

To find --> Terms > greater than 10

K can be +ve or -ve
We have Info of "N"

Statement 1:
we don't know about "k"..
Insufficient

Statement 2:
A8 = 10
We have info of "N" .. 8th is the middle term.. so "7 terms" is the answer
SUFFICIENT,

Answer [spoiler]{B}[/spoiler]
Last edited by theCodeToGMAT on Sat Oct 05, 2013 12:06 am, edited 1 time in total.
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by rakeshd347 » Fri Oct 04, 2013 11:53 pm
theCodeToGMAT wrote:
rakeshd347 wrote:Given a sequence: a1,a2,a3,a4......
In the sequence shown,an=(an-1)+k , where and k is a nonzero constant. How many of the terms in the sequence are greater than 10?

(1) a1=24
(2) a8=10
To find --> Terms > greater than 10

K can be +ve or -ve
NO Info of "N"

Statement 1:
we don't know about "k"..
Insufficient

Statement 2:
A8 = 10
No info of "N"
INSUFFICIENT,

Combining...
Sufficient.

Answer [spoiler]{C}[/spoiler]

What is the OA???
This one is tricky and tough. Try again wrong answer.
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by rakeshd347 » Fri Oct 04, 2013 11:57 pm
rakeshd347 wrote:
theCodeToGMAT wrote:
rakeshd347 wrote:Given a sequence: a1,a2,a3,a4......
In the sequence shown,an=(an-1)+k , where and k is a nonzero constant. How many of the terms in the sequence are greater than 10?

(1) a1=24
(2) a8=10
To find --> Terms > greater than 10

K can be +ve or -ve
NO Info of "N"

Statement 1:
we don't know about "k"..
Insufficient

Statement 2:
A8 = 10
No info of "N"
INSUFFICIENT,

Combining...
Sufficient.

Answer [spoiler]{C}[/spoiler]

What is the OA???
This one is tricky and tough. Try again wrong answer.
Sorry my bad. i missed one part of the question try again.
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by theCodeToGMAT » Sat Oct 05, 2013 12:05 am
rakeshd347 wrote: Sorry my bad. i missed one part of the question try again.
ohk :), then the Answer must be [spoiler]{B}[/spoiler]
Solution Updated!
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by GMATGuruNY » Sat Oct 05, 2013 3:42 am
a(1), a(2),...., a(15)
In the sequence shown, a(n) = a(n-1) + k, where 2≤n≤15 and k is a nonzero constant. How many of the terms in the sequence are greater than 10?

1) a(1)=24
2) a(8)=10
Statement 1 is clearly insufficient.

Statement 2: a₈ = 10.
If k>0, then the sequence is INCREASING: each term in the sequence is GREATER than the preceding term.
In this case, a₉...a�₅ -- a total of 7 terms -- will be greater than 10.
If k<0, then the sequence is DECREASING: each term in the sequence is LESS than the preceding term.
In this case, a�...a₇ -- a total of 7 terms -- will be greater than 10.
In each case, the number of terms greater than 10 = 7.
SUFFICIENT.

The correct answer is B.
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