# urgent need help on conditional probability.

• Nov 16th 2009, 10:53 AM
john12345
urgent need help on conditional probability.
Question:

In acertain region of the country if is known from past experience that the probability of selecting an adult over 40 years old age with cancer 0.05 . If the probability of adoctor diagnosing aperson with cancer having the diases is 0.78 and the probability of incorrectly diagnosing aperson without cancer as having the dieses is 0.06:

1-what is the probability that aperson diagnised having acancer

2-what is the probability as having acancer actually has adieses.

thanks alot
• Nov 16th 2009, 07:45 PM
mr fantastic
Quote:

Originally Posted by john12345
Question:

In acertain region of the country if is known from past experience that the probability of selecting an adult over 40 years old age with cancer 0.05 . If the probability of adoctor diagnosing aperson with cancer having the diases is 0.78 and the probability of incorrectly diagnosing aperson without cancer as having the dieses is 0.06:

1-what is the probability that aperson diagnised having acancer

2-what is the probability as having acancer actually has adieses.

thanks alot

Draw a tree diagram. The first two branches are C and C' (where C = has cancer). Then:

1. (0.05)(0.78) + (0.95)(0.06)

2. $\frac{(0.05)(0.78)}{(0.05)(0.78) + (0.95)(0.06)}$