Data Sufficiency

Hi, just when i was reviewing this question in Data sufficiency in pg 283... Q 98

Is rst=1?

1)rs=1
2)st=1

Even though the answer key says its E...both statements are not sufficient, if dont find the answer convincing..


According to me my answer is C both statement together is sufficient. PFB my view

from statement 1: rs=1
r=(1/s)....(a)

from statement 2: st=1
t=(1/s)....(b)

sub both (a) & (b) in rst=1

=> (1/s)*s*(1/s)=1
=>(1/s)=1
=>s=1

substituting s=1 in (a) & (b) we can arrive at r=1 & t=1

which can clearly tell us rst=1

Hence i selected answer choice C...both equations together are sufficient to solve the target question but neither alone is sufficient.


Please help clarify how the OG arrives to ans choice E.
Highly appreciated. Thanks in advance.

Cheers,
Karthi Sarvendiran.

karthisarvendiran wrote: Is rst=1?

1)rs=1
2)st=1

Hi karthisarvendiran,

Also, do note that the question doesn't provide any limits on r, s and t. They could be anything : fractions, integers etc. So you have to consider all of these when answering the question.