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If we want a chance of 5% or less that a person will

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CTO
Joined: 19 Dec 2002
Posts: 250
Location: Ukraine
If we want a chance of 5% or less that a person will [#permalink]

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28 Apr 2003, 11:20
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If we want a chance of 5% or less that a person will encounter any question twice (in first and second test) in two consequtive random selections of 40 questions out of a question bank, how large should this question bank be?

I fear you need Excel to solve this one.
SVP
Joined: 03 Feb 2003
Posts: 1604

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05 May 2003, 00:05
x is the number of questions in the bank. The probability of having at least one question in two selections of 40 = 1 - [(x-40)C40/xC40]

It should be less than or equal to 0.05.

1 - [(x-40)C40/xC40]<=0.05

Excel says that x should be about 31000. P=0.0503.
CTO
Joined: 19 Dec 2002
Posts: 250
Location: Ukraine
21 years to develop [#permalink]

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06 May 2003, 04:26
thanks

Right now we have capacity of 4 questions a day, which means developing such a bank will take 21 years.

Ok, this means we need software that would remember which questions you already answered...
SVP
Joined: 03 Feb 2003
Posts: 1604

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06 May 2003, 05:05
The number of questions in your bank should increse exponentially. In this case it should take much less time. :D
CTO
Joined: 19 Dec 2002
Posts: 250
Location: Ukraine

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06 May 2003, 05:35
Great idea, stolyar!

If bb got $1 mln, we could launch a campaign - get$10 for every question you prepared, + $1 for each question your friends prepared, so that people could use a multi-level marketing, to get an exponent Founder Joined: 04 Dec 2002 Posts: 15143 Location: United States (WA) GMAT 1: 750 Q49 V42 Re: great idea [#permalink] Show Tags 10 May 2003, 20:54 gravedigger wrote: Great idea, stolyar! If bb got$1 mln, we could launch a campaign - get $10 for every question you prepared, +$1 for each question your friends prepared, so that people could use a multi-level marketing, to get an exponent

Great Idea. I really love it... can we drop the second part and leave me with \$1 mln?
Re: great idea   [#permalink] 10 May 2003, 20:54
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If we want a chance of 5% or less that a person will

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