@Arun: The probability of getting a head on the first toss is 1/5 * 1 + 4/5 * (1/2) ) = 3/5, while the probability of getting 2 consecutive heads is 1/5 * 1 + 4/5 * (1/2)^2 ) = 2/5. Thus, the probability of getting a head on the second roll given that you have gotten a head on the first roll is (2/5) / (3/5), which is 2/3.
If you didn't know the outcome of the first roll, the probability of heads on the second roll would still be 3/5. Dave On Aug 9, 2:57 am, Arun Vishwanathan <aaron.nar...@gmail.com> wrote: > @dave: yes it seems so that 17/18 is correct...I deduced it from the cond > prob formula.. > > I have a minor doubt in general ....why prob( 2nd toss is a head given that > a head occurred in the first toss ) doesnt seem same as p( head in first > toss and head in second toss with fair coin) +p(head in first toss and head > in second toss with unfair coin)? is it due to the fact that we are not > looking at the same sample space in both cases?i am not able to visualise > the difference in general..this is also the reason why most of the people > said earlier 17/80 as the answer.... > > moreover, if the question was exactly the same except in that it was NOT > mentioned that heads occurred previously , what would the prob of getting a > head in the second toss? > > would it be P( of getting tail in first toss and head in second toss given > that fair coin is chosen) +P( of getting head in first toss and head in > second toss given that fair coin is chosen) +P( getting heads in first toss > and heads in second toss given that unfair coin is chosen) ? this for any > toss turns out to be 3/5 ....can u explain the logic abt why it always gives > 3/5? > > On Tue, Aug 9, 2011 at 7:37 AM, raj kumar <megamonste...@gmail.com> wrote: > > plz reply am i right or wrong > > > -- > > You received this message because you are subscribed to the Google Groups > > "Algorithm Geeks" group. > > To post to this group, send email to algogeeks@googlegroups.com. > > To unsubscribe from this group, send email to > > algogeeks+unsubscr...@googlegroups.com. > > For more options, visit this group at > >http://groups.google.com/group/algogeeks?hl=en. > > -- > "People often say that motivation doesn't last. Well, neither does bathing > - that's why we recommend it daily." -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
