# Learn By Doing – Probability Rule Four

Published: January 8th, 2013

Category: Activity 1: Learn By Doing

Recall the blood type example:

• A person with type A can donate blood to a person with type A or AB.
• A person with type B can donate blood to a person with type B or AB.
• A person with type AB can donate blood to a person with type AB only.
• A person with type O blood can donate to anyone.

Suppose that there are two patients who are each in need of a blood donation. Patient 1 has blood type A and patient 2 has blood type B. Consider randomly selecting a person (to be a blood donor) and define the following events:

• D1 — the randomly chosen person can be a donor for patient 1.
• D2 — the randomly chosen person can be a donor for patient 2.

http://phhp-faculty-cantrell.sites.medinfo.ufl.edu/files/2012/12/LBD_06004_103.swf

http://phhp-faculty-cantrell.sites.medinfo.ufl.edu/files/2012/12/LBD_06005_103.swf

## Hint

http://phhp-faculty-cantrell.sites.medinfo.ufl.edu/files/2012/12/LBD_06006_103.swf

This document is linked from Basic Probability Rules.