# Thread: urgent need help on conditional probability.

1. ## 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

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