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May 12th, 2013, 03:12 AM   #1
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Probability problem

OK so there's 80 light bulbs
6 are defective, which means 74 are not defective.
If I select 2 at random, what are the odds at least one is defective.

the answer key says. 1- C(74,2)/ C(80,2) = 1- 74x73/80x79 = .145


I don't understand the answer key at all. I thought to use a stem-graph ( a line with more lines protruding from that line, shwoing the varous probabilites of otcomes.))

can someone explain please?
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May 12th, 2013, 04:51 AM   #2
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Re: Probability problem

Hello, hamburgertime!

Quote:
There are 80 light bulbs: 6 are Defective, 74 are Good.
If I select 2 at random, what is the probability at least one is Defective.

The answer key says:[color=beige] .[/color]

Can someone explain please?

The opposite of "at least one defective? is "NO defective".

What is the probability of no Defective (both are Good)?

There are:[color=beige] .[/color] possible pairs of bulbs.
There are:[color=beige] .[/color] pairs of Good bulbs.







~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~


It could be solved like this . . .

There are three possible scenarios:







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