how many

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- Aug 25th 2007, 01:58 AMshirelprobability/expected value exercise
how many

- Aug 25th 2007, 03:16 AMCaptainBlack
- Aug 25th 2007, 03:20 AMCaptainBlack
Whether you suspect that a coin is unfair if it fails a test that a fair coin

passes 90% of the time depends on you, do you have some other reasom to

suspect the coin? Otherwise you may suspect it and possibly do somemore tests.

If it fails a 99% test you may have more reason to suspect the coin.

RonL - Aug 25th 2007, 04:57 PMSoroban
Hello, shirel!

Another (slightly different) explanation . . .

Quote:

How many times does one have to roll a die in order

to have face 5 showing up with a 90% certainty?

We know that for one roll: .

Consider consecutive rolls__without__a 5.

. . This probability is: .

And we want this probability to be less than 10%.

. . Hence, we have: .

Take logs: .

. . Divide by which is**negative**: .

Therefore, one must roll a die at least 13 times.