Independent solution

How to solve this Set Probability question

Setup

Setup

Use the event definitions to identify the relevant set relationships.

BA,AC=,BC=B\subset A,\qquad A\cap C=\varnothing,\qquad B\cap C=\varnothing

Model

Model

A union with a subset equals the larger event. A union of disjoint events has probability equal to the sum of their probabilities.

Pr(AB)=Pr(A)\Pr(A\cup B)=\Pr(A)
Pr(AC)=Pr(A)+Pr(C)\Pr(A\cup C)=\Pr(A)+\Pr(C)
Pr(BC)=Pr(B)+Pr(C)\Pr(B\cup C)=\Pr(B)+\Pr(C)

Compute

Compute

Substitute the three supplied event probabilities.

Pr(AB)=0.30\Pr(A\cup B)=0.30
Pr(AC)=0.30+0.70=1.00\Pr(A\cup C)=0.30+0.70=1.00
Pr(BC)=0.10+0.70=0.80\Pr(B\cup C)=0.10+0.70=0.80
0.30+1.00+0.80=2.100.30+1.00+0.80=2.10

Answer

Answer

The requested sum of union probabilities is 2.10.

2.10(C)\boxed{2.10\quad\text{(C)}}