Independent solution

How to solve this Law of Total Probability question

Setup

Setup

Convert the class counts to proportions and complement the two no-hospitalization rates.

Pr(A)=0.40,Pr(B)=0.60\Pr(A)=0.40,\qquad \Pr(B)=0.60
Pr(HA)=0.02,Pr(HB)=0.005\Pr(H\mid A)=0.02,\qquad \Pr(H\mid B)=0.005

Model

Model

Weight each class-specific hospitalization rate by its class proportion.

Pr(AH)=(0.40)(0.02)=0.008\Pr(A\cap H)=(0.40)(0.02)=0.008
Pr(BH)=(0.60)(0.005)=0.003\Pr(B\cap H)=(0.60)(0.005)=0.003

Compute

Compute

Condition the Class A contribution on the total hospitalization probability.

Pr(AH)=0.0080.008+0.003=811=0.727272\Pr(A\mid H)=\frac{0.008}{0.008+0.003}=\frac8{11}=0.727272\ldots

Answer

Answer

A hospitalized policyholder has probability approximately 0.727 of belonging to Class A.

0.727(E)\boxed{0.727\quad\text{(E)}}