A coin is tossed three times in succession. If `E`
is the
event that there are at least two heads and `F`
is the
event in which first throw is a head, then find `P(E//F)dot`
If a coin is tossed three times, then the sample S is
`S={HHH,HHT, HTH, HT T ,THH,THT, T TH, T T T }`
`thereforen(S)=8.`
(i) `A={HHH, HTH, THH, T TH]`...
`P(E_(1))=1-["P(all heads)+P(all tails")]`
`=1-[(1)/(2^(n))+(1)/(2^(n))]=1-(1)/(2^(n-1))`
`P(E_(2))=P("no head)+P(exactly one head")`
`=(1)/(2^(n))+^(""n)C_(1).(1)/(2^(n))=(n)/(2^(n))`
`P(E_(1)nnE_(2))=("exactly one head and"(n-1)till)`
`=^(""n)C_(1).(1)/(2).(1)/(2^(n-1))=(n)/(2^(n))`
If `E_(1)and E_(2)` are indipendent, then
`P(E_(1)nnE_(2))=P(E_(1)).P(E_(2))`
`implies(n)/(2^(n))=(1-(1)/(2^(n-1)))((n+1)/(2^(n)))`
`impliesn=(1-(1)/(2^(n-1)))(n+1)`
Correct Answer - C
The required probability is
1- probability of getting equal number of heads and tails
`=1-""^(2n)C_(n)((1)/(2))^(n)((1)/(2))^(2n-n)`
`=1-((2n)!)/((n!)^(2))xx(1)/(4^(n))`
Correct Answer - 2
Here `P(E)=1/2and P(F_(k))=""^(n)C_(k).(1)/(2^(n))`
Also, `P(EnnF_(k))=p` (exactly k heads are obtained and head obtained in first filp)
`=1/2""^(n-1)C_(k-1)((1)/(2))^(n-1)`
Events E and `f_(k)` are independent. Therefore,
`P(EnnF_(k))=P(E).P(F_(k))`
`or ""^(n-1)C_(k-1)xx(1)/(2^(n))=1/2xx""^(n)C_(k)(1)/(2^(n))`...
Correct Answer - C
`(c )` The cases for `a_(1){H,T}` i.e, `a_(1)=2`
The cases for `a_(2){HT,TH,TT}`, `a_(2)=3`
For `n ge 3` , if the first outcome is `H`, then next just...