Is st = t ? (1) s = st (2) t = ts

Question

Is st = t ?

(1) s = st

(2) t = ts

Bunuel · Answer

Is st = t ?

Is  st = t ? --> is  s=1  or  t=0  (or both)?

(1) s = st -->  s=0  or  t=1  (or both). Not sufficient.

(2) t = ts. Directly answers the question. Sufficient.

Answer: B.

12Sums · Answer

Hi Bunuel,

from st (1) : we know that 's' not equals 1 or 't' not equals 0 or both , so is this st not sufficient alone.

Pls clarify

Bunuel · Answer

Consider this:
If  s=0  and  t
eq{0}  ( s = st ), then  st
eq{t} . Or if  t=1  and  s
eq{1}  ( s = st ), then  st
eq{t} . So, for these cases the answer to the question is NO.

If  s=t=0  ( s = st ), then  st={t} . Or if  s=t=1  ( s = st ), then  st={t} . So, for these cases the answer to the question is YES.

Does this make sense?

12Sums · Answer

Yes Bunuel, when we consider values it makes sense.
But I am unable to get to this directly with out plugging values.

daviddaviddavid · Answer

For (1)

could be also assume following cases ?

case 1: s=t=0 then s=st

case 2: s=5,t=1 then s≠st

thanks =)

Raksat · Answer

@bunnel If we have a statement that restates the question , then it becomes insufficient as we don't have any additional information to answer the question. But here the equality nullifies it and directly answers the question. Hence it is sufficient. IS this reasoning correct ?
i

Bunuel · Answer

Not sure I can follow you.

Say the question asks: is x = 1? And (1) says that x = 1. In this case (1) is sufficient as it directly answers the question: YES x does equal to 1. This is EXACTLY the case we have with the above question.

Raksat · Answer

Its about the difference between a tautological statement and this question. Reference question : https://gmatclub.com/forum/in-the-diagr ... 94414.html In the explanation you explained " This statement repeats information in the prompt, and contains no new information, so it doesn’t help us at all to figure out anything else. This statement, alone and by itself, is not sufficient." Here B is also reintroducing the information in question. what's the difference ?

Bunuel · Answer

In the question you quote one of the statements says something that is generally true, so it adds not new info. It says something like x = x, that is generally true.

Here the question asks is  st = t ? (2) says t = ts. So, it gives an YES answer to the question.

kmilen · Answer

But then for statement 1 isn't the answer 'definitely no' and therefore sufficient?

whatisthematrix · Answer

What a sneaky question. Fact 2 is literally the originally question but in reverse. It answers itself. SNEAKY!! I'm starting to see the ridiculousness of GMAT questions

Posted from my mobile device

kittle · Answer

Under Algebra what is the sub-topic for this? Thanks.

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Is st = t ? (1) s = st (2) t = ts

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