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series and permutation and combination

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series and permutation and combination

by abhinav khanna » Mon Feb 13, 2012 5:47 am
Hi all kindly guide me to the solution for these D.S questions

1) Sequence S consists of 24 non zero integers if each term in S after the second is the product of previous two terms then How many terms are there in Sequence S.

a) Third term in S is positive.
b) Fourth term in S is negative.



2) 12 Jurors must be picked from a pool of n potential jurors. If m of the potential jurors are rejected by defense counsel then how many different possible jurors could be picked from the remaining potential jurors.

a) If one less potential juror had been rejected then it would have been possible to create 13 different juries.
b) n = m+2

Regards
Abhinav
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by Jim@StratusPrep » Mon Feb 13, 2012 6:52 am
I assume for the #1 that you are asked how many positive or negative terms there are in the sequence...


1) The sequence could start +, +, + or -, -, + ... Insufficient
2) Sequence would look like this -, +, -, - or -, -, +, - .... Insufficient

Putting them together, if must be -, -, +, - and you could figure out all other terms.

ANSWER: C

Statement is looking for you to find the following combination (n-m)!/12!(n-m-12)!

1)if you replace n-m with x you get x!/12!(x-12)! and you want to find a value for x that creates 13 jurys. Usually, you wont have to hunt too hard so let's try 13.... 13!/12!1! = 13. This would mean that x actually equals 14 and you could get the number of jurys. SUFFICIENT

2) Could be any combination of n and m.... Insufficient

Answer: A
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by lephuong » Mon Feb 13, 2012 8:49 am
B is correct though.

Since the fourth term is negative, we have 2 options:
- 3rd term is negative; 2nd term is positive
- 3rd term is positive; 2nd term is negative

If we write a diagram, it would look like this (i know this is not a diagram, I just want to illustrate the 24 terms ;)

Option 1:
1 -, 2 -, 3 +, 4 -, 5 -, 6 +, 7 -, 8 -, 9 +
Option 2:
1 -, 2 +, 3 -, 4 -, 5 +, 6 -, 7 -, 8 +, 9 -

Both options follow the same pattern: negative : positive = 2:1. With each of these we end up with 8 negatives.
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by [email protected] » Wed Feb 15, 2012 10:00 pm
Jim@StratusPrep!!!

The correct answer for the 1st question i.e 1) Sequence S consists of 24 non zero integers if each term in S after the second is the product of previous two terms then How many terms are there in Sequence S.

a) Third term in S is positive.
b) Fourth term in S is negative.

The answer is B. Take any combination that you gave and you find that the answer turns out to be 8 positive terms and 16 negative terms...


You do not require both the statements though for the same figure...

Hence the OA should be B, Abhinav what is the OA...
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by abhinav khanna » Fri Feb 17, 2012 9:29 am
hey amit, you are right the answer is b and answer for second question is d, sorry for the delay
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by ArunangsuSahu » Fri Feb 17, 2012 11:34 am
The fourth term defines the series.

(B) is the answer
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by kwhite » Sat Feb 25, 2012 12:22 am
delete.
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by abhinav khanna » Tue Feb 28, 2012 7:52 am
hey kwhite, It's very possible to have errors on any of the reference books. but i don't have a very good grasp on this so can't say anything.
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