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# lights

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Joined: 18 May 2008
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lights [#permalink]  13 Feb 2009, 03:33
Eighty percent of the lights at Hotel California are on at 8 p.m. a certain evening. However, forty percent of the lights that are supposed to be off are actually on and ten percent of the lights that are supposed to be on are actually off. What percent of the lights that are on are supposed to be off?

Ans:10%
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Re: lights [#permalink]  13 Feb 2009, 04:27
ritula wrote:
Eighty percent of the lights at Hotel California are on at 8 p.m. a certain evening. However, forty percent of the lights that are supposed to be off are actually on and ten percent of the lights that are supposed to be on are actually off. What percent of the lights that are on are supposed to be off?

Ans:10%

take total lights as 100

light curently ON : 80

let lights supposed to be ON = x
supposed to be off = y

So .4x + .9y = 80 --------- 1)
Also we know x + y = 100 --- 2) since percentage

solving equation we get,

x = 20 and y = 80

from question,40% of X is ON which is supposed to be OFF

So i am getting 8%
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Re: lights [#permalink]  13 Feb 2009, 04:38
Hi Selvae,

since supposed to be on light y = 80.

the qusetions ask what percent of supposed to be on lights are off.

so it is 8/80 * 100 = 10%.

Correct me if i am wrong.
Re: lights   [#permalink] 13 Feb 2009, 04:38
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