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Manhattan test 3 - DS doubt

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Manhattan test 3 - DS doubt

by shivani.magan » Wed Mar 07, 2012 10:30 am
Is the product st negative?

(1) s2 - s < 0
(2) s-4/t-3 = 1


A.Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B.Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C.Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient.
D.EACH statement ALONE is sufficient.
E.Statements (1) and (2) TOGETHER are NOT sufficient.
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Source: — Data Sufficiency |
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by killer1387 » Wed Mar 07, 2012 10:40 am
shivani.magan wrote:Is the product st negative?

(1) s2 - s < 0
(2) s-4/t-3 = 1
1. 0<s<1, insuff
2. s=t+1 (assuming the written relation is (s-4)/(t-3), do use brackets to remove ambiguity)
insuff.
1 & 2
-1<t<0
hence sufficienct

thus C
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by nakul.maheshwari » Thu Mar 08, 2012 3:11 pm
Wait a minute..is it (s-4)/(t-3) = 1 or s-(4/t)-3 = 1;

If it is (s-4)/(t-3), shouldnt the answer be B?

s-4 = t - 3
s-t = 1

If s = +ve, then t = +ve
If s = -ve, then t = -ve
S and t cannot have opposite values, hence s.t is never negative.

Answer B? what am i missing here?
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by nakul.maheshwari » Thu Mar 08, 2012 3:20 pm
Never mind, just realized that 't' can be "0" also
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by ranjeet75 » Fri Mar 09, 2012 9:08 am
I think E should be the answer.

Stat 1: S(s - 1) < 0
so, either s < 0 or s < 1

Insuff as we don't know abt t

Stst 2: s - 4 = t - 3

s = 1+t but s and t both can be either +ve or -ve.

Both: s = 0.9 so, t = - 0.1, so st = -ve
s = 4 so, t = 3, st = +ve
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by shivani.magan » Sat Mar 10, 2012 3:25 am
ranjeet75 wrote:I think E should be the answer.

Stat 1: S(s - 1) < 0
so, either s < 0 or s < 1

Insuff as we don't know abt t

Stst 2: s - 4 = t - 3

s = 1+t but s and t both can be either +ve or -ve.

Both: s = 0.9 so, t = - 0.1, so st = -ve
s = 4 so, t = 3, st = +ve
but s cannot be 4 because s<0 or s<1
however s can be negative . if s - -2 then since s= t+1 t = -1 and st becomes positive. what i am doing wron here?
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by shivani.magan » Sat Mar 10, 2012 3:26 am
killer1387 wrote:
shivani.magan wrote:Is the product st negative?

(1) s2 - s < 0
(2) s-4/t-3 = 1
1. 0<s<1, insuff
2. s=t+1 (assuming the written relation is (s-4)/(t-3), do use brackets to remove ambiguity)
insuff.
1 & 2
-1<t<0
hence sufficienct

thus C

Can u see above and tell me what am i doing wrong here?
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by killer1387 » Sat Mar 10, 2012 4:05 am
shivani.magan wrote: but s cannot be 4 because s<0 or s<1
however s can be negative . if s - -2 then since s= t+1 t = -1 and st becomes positive. what i am doing wron here?
Is the product st negative?

(1) s2 - s < 0
(2) s-4/t-3 = 1

The part in bold is wrong
from
(1)s2 - s < 0
0<s<1
so s is positive.--> insufficient

(2) s=t+1
insufficient
from 1 & 2

s is positive
and
0<t+1<1
i.e. -1<t<0
i.e. t is negative

hence st is negative
sufficient.
so C

Hope this clarifies.
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by killer1387 » Sat Mar 10, 2012 4:11 am
nakul.maheshwari wrote:Wait a minute..is it (s-4)/(t-3) = 1 or s-(4/t)-3 = 1;

If it is (s-4)/(t-3), shouldnt the answer be B?

s-4 = t - 3
s-t = 1

If s = +ve, then t = +ve
If s = -ve, then t = -ve
S and t cannot have opposite values, hence s.t is never negative.

Answer B? what am i missing here?
the part in bold is wrong.
(2)
t=s-1
If s = +ve, then t = can be both +ve and -ve
i.e. for 0<s<1 => t<0
for 1<s<infinity => t>0
so insufficient

HTH
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by teal » Sun Mar 11, 2012 10:10 am
Stat 2 says s = t+1; There are three possibilities a) one of them can be zero and the other either positive or negative; b) both can positive c) both can be negative

In either of these three cases product st will be either positive or zero so the answer will be NO

Wouldn't that mean B as the answer? Can someone please give me a case when product st will be negative given the conditions of statement (2).
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