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Lights on.. lights off

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Lights on.. lights off

by dumb.doofus » Mon May 18, 2009 10:31 pm
Eighty percent of the lights at Hotel California are switched on at 8 p.m. one evening. However, forty percent of the lights that are supposed to be switched off are actually switched on, and ten percent of the lights that are supposed to be switched on are actually switched off. What percent of the lights that are switched on are supposed to be switched off?

22(2/9)%
16(2/3)%
11(1/9)%
10%
5%
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by scoobydooby » Mon May 18, 2009 10:42 pm
am getting 10%

set it up in a 2 by 2 matrix.
let total lights be 100, 80 actually switched on, 20 actually switched off.
let x be expected to be switched off, 100-x expected to be switched on.

0.4x+0.9(100-x)=80.....1
solving we get x=20

expected to be off/actually on=0.4*20/80=10%

hence, D
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by Svedankae » Tue May 19, 2009 1:53 am
what would that 2x2 matrix for yours look like?
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by scoobydooby » Tue May 19, 2009 2:02 am
here you go
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by dumb.doofus » Tue May 19, 2009 3:38 pm
Well done, ScoobyDooby..
One love, one blood, one life. You got to do what you should.
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