# Thread: Probability

1. ## Probability

The probability is 0.1 of a land containing oil, but before you drill you ask a geologist who will tell if the prospects are good or not good but she is not perfect so If there is no oil, the conditional probability that the prospects are good is 0.9. If there is no oil, the conditional probability that the prospects are not good is 0.85

So given that the prospects are good what is the probability that you will find oil??

Quite long and please help me urgent and tell me detailed way please or even a quicker way to check answers

Like any tips/tricks in Probability

Answer:0.4

2. Originally Posted by someone21
The probability is 0.1 of a land containing oil, but before you drill you ask a geologist who will tell if the prospects are good or not good but she is not perfect so

If there is no oil, the conditional probability that the prospects are good is 0.9. Mr F says: Surely you mean "If there is oil, the conditional probability that the prospects are good is 0.9" ......

If there is no oil, the conditional probability that the prospects are not good is 0.85

So given that the prospects are good what is the probability that you will find oil??

Quite long and please help me urgent and tell me detailed way please or even a quicker way to check answers

Like any tips/tricks in Probability

Answer:0.4
Here's a tip: A tree diagram makes things very clear.

$\Pr(O | G) = \frac{(0.1)(0.9)}{(0.1)(0.9) + (0.9)(0.15)}$