Answer A. Simple question.

Let total Rooms = 100x

Let a : Only TV
Let b : Both TV and AC
Let c : Only AC.

As per Venn Diagram Rule, We have a + b + c =100x and b + c = AC rooms = 30x

=> a = 70x.

We need to find out % of b.

Statement 1 : a + b = TV Rooms = 80x

or we can say b = 10x = 10%

SUFFICIENT.

Statement 2 : a = 70x. No new information. We already know a is 70x. Hence, insufficient.

Answer A.
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yes, correct. So, I have taken b+c = 30x.

Added the initial line by mistake. The approach and the solution is correct. I have removed that line now. "We are given c = 30x"
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At a certain hotel, every room has air conditioning or cable TV or both. If 30 percent of the rooms have air conditioning, what percent of the rooms have air conditioning and cable TV?

(1) 80 percent of the rooms have cable TV
(2) 70 percent of the rooms have cable TV but not air conditioning

1: A is sufficient
Total = A + T - AT
100 = 30 +80 -AT
AT = 10%

Sufficient

2:

Total= A only + T only +AT
100 = A only + 70 +AT
100 = A - AT +70 +AT
100 = A + 70
A = 30...that we already knows

Not able to find AT = ???

Hence information is not sufficient.

Answer is A