3 votes 3 votes an unbiased coin is tossed infinite no of times.The probability that 4th head appear at 10th toss is 1) 0.067 2) 0.073 3) 0.082 4) 0.091 Probability probability + – Pooja Palod asked Dec 16, 2015 • edited Dec 16, 2015 by Pooja Palod Pooja Palod 5.3k views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
Best answer 8 votes 8 votes We can say 10th toss is a head In previous 9 toss ,we have to take 6 tail and 3 head with probability =(9)! / (6! *3! ) = (9*8*7)/(3*2) =3*4*7 = 84 Now, probability of 10 th toss will be head = 84/ 210 =21/256 =0.082 Answer will be (3) srestha answered Dec 16, 2015 • selected Dec 25, 2015 by Pooja Palod srestha comment Share Follow See all 5 Comments See all 5 5 Comments reply Show 2 previous comments Shivateja MST commented Dec 11, 2019 reply Follow Share @srestha I have a doubt. If we try like distributing four heads to first 10 tosses and then from those cases removing the cases that have all four heads in first 9 tosses,then this approach also should give same result right? Or are there any cases that could be missed in this approach. please clarify. 0 votes 0 votes srestha commented Dec 11, 2019 reply Follow Share then $\frac{10!}{4!6!}$ 0 votes 0 votes Shivateja MST commented Dec 11, 2019 reply Follow Share But I got like C(10,4)*(0.5)^4 *(0.5)^6 - C(9,4) *(0.5)^4 *(0.5)^5 0 votes 0 votes Please log in or register to add a comment.
4 votes 4 votes In 9 tosses we need 3 heads.... (9c3/2^9)*(probability of 10th toss) =(9c3/2^9)*(1/2)=0.082 papesh answered Feb 20, 2016 papesh comment Share Follow See all 4 Comments See all 4 4 Comments reply Aboveallplayer commented Aug 14, 2016 reply Follow Share @gabbar i like your approach more than the selected answer, but can you tell me one thing while selecting 3 heads we are doing 9c3/2^9 that i understand but as we are selecting heads which itself has a probability of (1/2) why we are not multyplying 1/2 with this...........forget about 10th head,, i got that part 0 votes 0 votes papesh commented Aug 14, 2016 reply Follow Share Here I have multiplied... (1/2 )^9 comes that way... 0 votes 0 votes Aboveallplayer commented Aug 14, 2016 reply Follow Share got it 0 votes 0 votes papesh commented Aug 14, 2016 reply Follow Share Thanks... I have problem with representation... 0 votes 0 votes Please log in or register to add a comment.