@dave - method is right, calculation mistake on my part, getting 17/18 only. thanks anyways.
On Aug 9, 6:26 pm, Dave <[email protected]> wrote: > @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 <[email protected]> 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 <[email protected]> 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 [email protected]. > > > To unsubscribe from this group, send email to > > > [email protected]. > > > 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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
