Answer:
0.2275 = 22.75% probability that you actually won that round
Step-by-step explanation:
Conditional Probability
We use the conditional probability formula to solve this question. It is
![P(B|A) = \frac{P(A \cap B)}{P(A)}](https://tex.z-dn.net/?f=P%28B%7CA%29%20%3D%20%5Cfrac%7BP%28A%20%5Ccap%20B%29%7D%7BP%28A%29%7D)
In which
P(B|A) is the probability of event B happening, given that A happened.
is the probability of both A and B happening.
P(A) is the probability of A happening.
In this question:
Event A: Fireworks going off
Event B: You won
Probability of fireworks going off.
100% of 1/35 = 0.0286(when you win)
10% of 34/35 = 0.9714(you lost). So
![P(A) = 0.0286 + 0.1*0.9714 = 0.12574](https://tex.z-dn.net/?f=P%28A%29%20%3D%200.0286%20%2B%200.1%2A0.9714%20%3D%200.12574)
Probability of you winning and fireworks going off:
100% of 1/35, so ![P(A \cap B) = 0.0286](https://tex.z-dn.net/?f=P%28A%20%5Ccap%20B%29%20%3D%200.0286)
If you failed to see the outcome of a round, but you see the fireworks going off, then what is the probability that you actually won that round?
![P(B|A) = \frac{P(A \cap B)}{P(A)} = \frac{0.0286}{0.12574} = 0.2275](https://tex.z-dn.net/?f=P%28B%7CA%29%20%3D%20%5Cfrac%7BP%28A%20%5Ccap%20B%29%7D%7BP%28A%29%7D%20%3D%20%5Cfrac%7B0.0286%7D%7B0.12574%7D%20%3D%200.2275)
0.2275 = 22.75% probability that you actually won that round