Take a look at the tree diagram. The first branching shows the probabilities of there being oil, or not being oil.
Then, for each case we consider the probabilities of the kit being accurate or not.
we are interested in the branch Oil---Kit accurate---
Since P(Oil)=0.45, and P(Kit accurate)=0.8, the probability of there being oil and the Kit showing it correctly is:
0.45*0.8=0.36.
Answer: C) 0.36
Then, for each case we consider the probabilities of the kit being accurate or not.
we are interested in the branch Oil---Kit accurate---
Since P(Oil)=0.45, and P(Kit accurate)=0.8, the probability of there being oil and the Kit showing it correctly is:
0.45*0.8=0.36.
Answer: C) 0.36
