[unreality]

You have a bag of 100 small balls. They are all shiny, black and identical except for a property called "zwahmness" which is extremely hard to detect (it has no effect on the physical appearance of the ball, at least that humans can detect with their senses).

You know that one of the balls is zwahm, the rest are fakes. You select a ball randomly from a bag...

Luckily you have a zwahmbo machine! The zwahmbo spits out 90% of zwahms and only 10% of fakes. It "retains" balls that it does not spit out.

You put in your selected ball and it spits it out!

(1) What is the probability that your ball is the zwahm ball?

(2) How many times as unlikely is the ball to be zwahm if it had been retained rather than spit out?

[Guest]

You have a bag of 100 small balls. They are all shiny, black and identical except for a property called "zwahmness" which is extremely hard to detect (it has no effect on the physical appearance of the ball, at least that humans can detect with their senses).

You know that one of the balls is zwahm, the rest are fakes. You select a ball randomly from a bag...

Luckily you have a zwahmbo machine! The zwahmbo spits out 90% of zwahms and only 10% of fakes. It "retains" balls that it does not spit out.

You put in your selected ball and it spits it out!

(1) What is the probability that your ball is the zwahm ball?

(2) How many times as unlikely is the ball to be zwahm if it had been retained rather than spit out?

that it would be 90% sorry if I'm wrong.

[Guest]

9:10 and 9 times?

it seems to simple to be true though

[Guest]

You have a bag of 100 small balls. They are all shiny, black and identical except for a property called "zwahmness" which is extremely hard to detect (it has no effect on the physical appearance of the ball, at least that humans can detect with their senses).

You know that one of the balls is zwahm, the rest are fakes. You select a ball randomly from a bag...

Luckily you have a zwahmbo machine! The zwahmbo spits out 90% of zwahms and only 10% of fakes. It "retains" balls that it does not spit out.

You put in your selected ball and it spits it out!

(1) What is the probability that your ball is the zwahm ball?

(2) How many times as unlikely is the ball to be zwahm if it had been retained rather than spit out?

90%*1% / (90%*1% + 99%*10%) =

1/12

Edited June 26, 2009 by hookemhorns

[unreality]

hookemhorns got it for #1 The previous two posters fell for the trap

#2 is yet to be solved ;D

[Guest]

hookemhorns got it for #1 The previous two posters fell for the trap

#2 is yet to be solved ;D

0.99887892376681614349775784753363

[Guest]

(1) What is the probability that your ball is the zwahm ball? - 0.9%

(2) How many times as unlikely is the ball to be zwahm if it had been retained rather than spit out? - 0.1%

Edited June 26, 2009 by KampK

[unreality]

0.99887892376681614349775784753363

(1) What is the probability that your ball is the zwahm ball? - 0.9%

(2) How many times as unlikely is the ball to be zwahm if it had been retained rather than spit out? - 0.1%

use spoilers, and neither is correct

hookemhorns got #1, #2 is as of now unsolved

[Prof. Templeton]

Is it 1.09 times as unlikely .9989/.9167. In other words you machine is useless

[unreality]

Is it 1.09 times as unlikely .9989/.9167. In other words you machine is useless

it's 74.33333333 times as unlikely ;D Unless I made a fatal error, #1 is 1/12, or 1/892 if it had retained it... 892/12 is 74.33333333

[Prof. Templeton]

what you were looking for. I gave you true negative(.9989) over false positive(.9167) and you wanted true positive(.0833) over false negative(.0011). I was reading "unlikely is the ball to be Zwahm" as likely to be fake and the machine retained it (true negative) or spit it out (false positive).

[unreality]

oh I see Yeah I see how the wording was ambigious

[Guest]

is it 75.167 times as unlikely?

[unreality]

p_m: close but no cigar