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7.34. For another approach to Theoretical Exercise 7.33, let Tr denote the number of flips required to obtain a run of r consecutive heads. (a) Determine E[Tr|Tr−1]. (b) Determine in terms of ·¡°Ú°Õ°ù−1±Õ. (c) What is E[T1]? (d) What is E[Tr]?

Short Answer

Expert verified

=1pET0=0

Step by step solution

01

Given Information 

Let be the probability that a coin lands on heads. Let Tr denote the number of flips required to obtain a run of r consecutive heads.

We have to find

E[Tr|Tr−1].

E[Tr−1]

E[T1]

E[Tr]

02

Explanation Of a

Letpbe the probability that a coin lands on heads. Let ETrdenote the number of flips required to obtain a run ofr consecutive heads.

Determine ETr∣Tr-1.

ETr∣Tr-1=Tr-1+1+(1-p)ETr

03

Explanation Of b

DetermineETf

Taking expectations on both sides of (a) yields,

ETr=ETr-1+1+(1-p)ETr

=1p+1pETr-1

04

Explanation Of c

DetermineSubstitute for r in part (b)

05

Explanation Of d

Determine ETr

ETr=1p+1pETr-1

=1p+1p1p+1pETr-1

=1p+1p2+1p2ETr-2

=1p+1p2+1p3+1p3ETr-3

=∑i=1p1pi+1prET0

=∑i=1r1piET0=0

06

Final Answer

ETr∣Tr-1=Tr-1+1+(1-p)ETr

·¡°Ú°Õ°ù−1±Õ. =1p+1pETr-1

E[T1]

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Most popular questions from this chapter

There are n items in a box labeled H and m in a box labeled T. A coin that comes up heads with probability p and tails with probability 1 − p is flipped. Each time it comes up heads, an item is removed from the H box, and each time it comes up tails, an item is removed from the T box. (If a box is empty and its outcome occurs, then no items are removed.) Find the expected number of coin flips needed for both boxes to become empty. Hint: Condition on the number of heads in the first n + m flips.

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