I'd pick Answer as D (10%)
Typical percent problem, so take total # of lights as 100. Now 80% of lights are currently ON or 80 lights
# of lights supposed to be ON = N
# of lights supposed to be OFF = F
Rewriting the sentence, you'd get (40/100)*F + N - (10/100)*N = 80.
Also, by our 100 light assumption, we can state F + N = 100
solving for F and N, you get F = 20 and N = 80. Hmmm...now I almost made a mistake here.
If you substitute this back, # of lights supposed to OFF that are ON = (40/100)* 20 which is 8. And # of lights supposed to ON that are OFF = (10/100)* 80 which is also 8.
anyways, the question is what % of lights that are ON that should be OFF.. so (8/80) * 100, which leaves us with a final answer that Hotel California is Energy In-effecient by 10%
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