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A test shows that 10 out of 100 gadgets are defective. If a random sample of two gadgets are chosen, the probability that both are defective is?
(10/100)² = 0.01 = 1%
Why did the vector cross the road?
It wanted to be normal.
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The study guide I'm using says the answer to this one is 1/110, so I guess I'm confused. I also thought this woud be 1/10 X 1/10 = 1/100 = 1%
If the first sentence means "There are 100 gadgets. 10 are defective." then the answer is
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Gotcha! Thanks to all of you.
The first answer (1%) is true if you are taking from a large population (say randomly sampling from your production run)
The second answer (1/110) is true if you are selecting from exactly 100 gadgets, and not replacing.
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
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I still really don't understand why it is 1/110. Please help.
Hi JoAnni;
MathsisFun's is with replacement and Avon's is without replacement.
Avon's post(# 4) is explained like this:
There are 10 bad picks out of the total 100 for the first choice:
after that there are 9 bad picks left out of 99 total picks for the second choice.
Now you just multiply 10/100 * 9/99 = 1/10 *1/11 = 1/110
Last edited by bobbym (2009-06-04 13:53:31)
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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