Sequence
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Source: Beat The GMAT — Data Sufficiency |
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cramya
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Stmt I
Given: x1 x2 x3 x4 ...... x24
The third term in S is positive i.e x3 is positive
x1 and x2 could bothe be positive or x1 and x2 could both be negative. This does not lead us to a 1 definite answer for the number of negative terms
INSUFF
Stmt II
The fourth term in S is negative i.e x4 is negative
This means either x3 is negative x2 positive
(OR)
x3 is POSITIVE x2 NEGATIVE
Case 1
x1 x2 x3 x4 x5 x6
+ve - ve -ve +ve -ve
or
Case2
x1 x2 x3 x4 x5 x6
-ve +ve -ve -ve +ve
If u notice after x5 the signs alternate and there are 20 left of which 10 will be negative and 10 positive
We now have to figure out x1-x4 signs
Case 1
x1 x2 x3 x4
-ve +ve - ve -ve
If its case1 then x1 has to be -ve
Case2
x1 x2 x3 x4
-ve -ve +ve -ve
If its case2 then x1 still has to be -ve since x2 is neagtive and x3 is positive
So whether its case 1 or case 2 we know in x1-x4 ther's 3 nagatives and 1 positive
1 DEFINITE ANSWER for the number of negative terms
SUFF
Let me know if u still have questions (m hoping the format came out right for the x's)
Good luck!
Given: x1 x2 x3 x4 ...... x24
The third term in S is positive i.e x3 is positive
x1 and x2 could bothe be positive or x1 and x2 could both be negative. This does not lead us to a 1 definite answer for the number of negative terms
INSUFF
Stmt II
The fourth term in S is negative i.e x4 is negative
This means either x3 is negative x2 positive
(OR)
x3 is POSITIVE x2 NEGATIVE
Case 1
x1 x2 x3 x4 x5 x6
+ve - ve -ve +ve -ve
or
Case2
x1 x2 x3 x4 x5 x6
-ve +ve -ve -ve +ve
If u notice after x5 the signs alternate and there are 20 left of which 10 will be negative and 10 positive
We now have to figure out x1-x4 signs
Case 1
x1 x2 x3 x4
-ve +ve - ve -ve
If its case1 then x1 has to be -ve
Case2
x1 x2 x3 x4
-ve -ve +ve -ve
If its case2 then x1 still has to be -ve since x2 is neagtive and x3 is positive
So whether its case 1 or case 2 we know in x1-x4 ther's 3 nagatives and 1 positive
1 DEFINITE ANSWER for the number of negative terms
SUFF
Let me know if u still have questions (m hoping the format came out right for the x's)
Good luck!
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cramya
- Legendary Member
- Posts: 2467
- Joined: Thu Aug 28, 2008 6:14 pm
- Thanked: 331 times
- Followed by:11 members
The formatting dint come out as expected so reposting it (removing x1)
Stmt II
The fourth term in S is negative i.e x4 is negative
This means either x3 is negative x2 positive
(OR)
x3 is POSITIVE x2 NEGATIVE
Forget x1 for the time being
Case 1
x2 x3 x4 x5 x6
+ve - ve -ve +ve -ve
or
Case2
x2 x3 x4 x5 x6
-ve +ve -ve -ve +ve
If u notice after x5 the signs alternate and there are 20 left of which 10 will be negative and 10 positive
We now have to figure out x1-x4 signs
Case 1
x1 x2 x3 x4
-ve +ve - ve -ve
If its case1 then x1 has to be -ve
Case2
x1 x2 x3 x4
-ve -ve +ve -ve
If its case2 then x1 still has to be -ve since x2 is neagtive and x3 is positive
So whether its case 1 or case 2 we know in x1-x4 ther's 3 nagatives and 1 positive
1 DEFINITE ANSWER for the number of negative terms
SUFF
Let me know if u still have questions (m hoping the format came out right for the x's)
Good luck!
Stmt II
The fourth term in S is negative i.e x4 is negative
This means either x3 is negative x2 positive
(OR)
x3 is POSITIVE x2 NEGATIVE
Forget x1 for the time being
Case 1
x2 x3 x4 x5 x6
+ve - ve -ve +ve -ve
or
Case2
x2 x3 x4 x5 x6
-ve +ve -ve -ve +ve
If u notice after x5 the signs alternate and there are 20 left of which 10 will be negative and 10 positive
We now have to figure out x1-x4 signs
Case 1
x1 x2 x3 x4
-ve +ve - ve -ve
If its case1 then x1 has to be -ve
Case2
x1 x2 x3 x4
-ve -ve +ve -ve
If its case2 then x1 still has to be -ve since x2 is neagtive and x3 is positive
So whether its case 1 or case 2 we know in x1-x4 ther's 3 nagatives and 1 positive
1 DEFINITE ANSWER for the number of negative terms
SUFF
Let me know if u still have questions (m hoping the format came out right for the x's)
Good luck!
