Is anyone really good at Statistics? :O

basilmarket.com forums : Chat | 7 posts archived

thread starter fight4friday Sep 28 2010 + PM | QUOTE | PERMALINK | REPORT

Ok, so i didnt go to school today, and my math teacher, being the nice guy that he is, let me take my math quiz home the day before. Im not quite sure what to do, so i figured id ask the brilliant minds of basil. :P A lie detector test catches 75% of all lies, unfortunately the machine makes the mistake of giving a false positive on 9% of all true statement. A) If Johnny answers 83% of all questions truthfully, what % accuses Johnny of lying? B) Given that the machine called it a lie, whats the probability that he was actually lying? well basil, can anyone help? free cookie for the right answer :D

My Characters: Fight4friday - 158 Broa Night Lord

harpieaxl 09/28/10 + PM | QUOTE | PERMALINK | REPORT

A)27% b) 83%

My Characters: Axoz - 90 Bera Outlaw

fight4friday 09/28/10 + PM | QUOTE | PERMALINK | REPORT

hmmm. but how?

My Characters: Fight4friday - 158 Broa Night Lord

j0s3a4d + PM | QUOTE | PERMALINK | REPORT

A. The machine is going to accuse of lying 75% of the times that he lies (.75*(1-.83) and 9* of the times he tells the truth (.83*.09) So p=.75*.17+.83*.09=.2022 B. 75% of the times he lies, the machine catches the lie. And 9% of the times he tells the truth the machine will say he lied. Therefore, if we do a number tree we can say that 75/(75+9)=probability of the machine being right if it says false. p=.892857 You can moderately trust my answer, I took AP Statistics last year and made a 5. I haven't done anything with it for the past 4 months but I still remember this stuff I think.

My Characters: iatLnbandLt - 107 Broa Chief Bandit

harpieaxl 09/28/10 + PM | QUOTE | PERMALINK | REPORT

well i don't know i know the answer but not how to do it sorry.

My Characters: Axoz - 90 Bera Outlaw

FragileFroob 09/28/10 + PM | QUOTE | PERMALINK | REPORT

b) 17% + (.83*0.25) = 37,75% ?

My Characters: Cracket - 92 Mardia I/L Mage

fight4friday 09/28/10 + PM | QUOTE | PERMALINK | REPORT

ok guys, i think i got it. Thanks all of you! special thanks to j0s3a4d!

My Characters: Fight4friday - 158 Broa Night Lord