I HAVE NO IDEA ON THIS ONE IM SO LOST

A geologist is using seismographs to test for oil. It is found that if oil is present, the test gives a positive result 95% of the time, and if oil is not present, the test gives a positive result 2% of the time. Oil is actually present in 1% of the cases tested. If the test shows positive, what is the probability that oil is present??????

(solved in either a tree diagram, contingency table or proper formula and substitution)

2. Originally Posted by jobear
I HAVE NO IDEA ON THIS ONE IM SO LOST

A geologist is using seismographs to test for oil. It is found that if oil is present, the test gives a positive result 95% of the time, and if oil is not present, the test gives a positive result 2% of the time. Oil is actually present in 1% of the cases tested. If the test shows positive, what is the probability that oil is present??????

(solved in either a tree diagram, contingency table or proper formula and substitution)

You need to get Pr(oil|+ve).

A tree diagram is the easiest approach to take.

$\frac{(0.01)(0.95)}{(0.01)(0.95) + (0.99)(0.02)} = .......$