The probability of getting n consecutive heads is
P(n heads) = 1/5 * 1 + 4/5 * (1/2)^n,
Thus, the probability of getting a head on the n+1st roll given that
you have gotten heads on all n previous rolls is
P(n+1 heads | n heads) = P(n+1) / P(n)
= ( 1/5 * 1 + 4/5 * (1/2)^(n+1) ) / ( 1/5 * 1 + 4/5 * (1/2)^n ).
Multiplying numerator and denominator by 5* 2^(n-1) and recognizing 4
as 2^2 gives
P(n+1 heads | n heads) = (2^(n-1) + 1) / (2^(n-1) + 2).

Dave

On Aug 9, 12:30 am, programming love <love.for.programm...@gmail.com>
wrote:
> @Dave: I guess 17/18 is correct. Since we have to *calculate the probability
> of getting a head in the 6th flip given that first 5 flips are a head*. Can
> you please explain how you got the values of consequent flips when you said
> this?
>
> *"In fact, the probability is 3/5 for the first flip. After a head is
> flipped, the probability of a head is 2/3. After two heads have been
> flipped, it is 3/4. After 3 heads, it is 5/6. After 4 heads, the
>  probability is 9/10, and after 5 heads, the probability is 17/18."*

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