Independent solution

How to solve this Binomial Distribution question

Setup

Setup

Let N count the covered occurrences across the five independent periods.

NBinomial(5,0.5)N\sim\operatorname{Binomial}(5,0.5)
B=30min(N,3)B=30\min(N,3)

Model

Model

Group all counts of three or more at the contractual payment limit.

E[min(N,3)]=k=02kPr(N=k)+3Pr(N3)E[\min(N,3)]=\sum_{k=0}^{2}k\Pr(N=k)+3\Pr(N\ge3)

Compute

Compute

Use the symmetric binomial probabilities with denominator 32.

E[min(N,3)]=5+20+3(10+5+1)32=7332E[\min(N,3)]=\frac{5+20+3(10+5+1)}{32}=\frac{73}{32}
E[B]=30(7332)=68.4375E[B]=30\left(\frac{73}{32}\right)=68.4375

Answer

Answer

The expected payment rounds to the listed value 68.

68(D)\boxed{68\quad\text{(D)}}