Consider a quiz where a person is given two questions and he must decide which question to answer first. Question 1 will be answered correctly with probability of 0.8 and the person will then receive as prize \$100, while question 2 will be answered correctly with probability 0.5, and the person will then receive as prize $200.
If the first question is answered incorrectly then the quiz terminates and that person is not allowed to attempt the second question.
What is the expected amount of money that can he win?
My solution
X – Random variable which denotes the amount of money won
X |
P(X=x) |
0$ |
0.5 +0.2 = 0.7 |
100$ |
0.8*0.5 = 0.4 |
200$ |
0.5*0.2 = 0.1 |
300$ |
0.8 |
P(X=0) = Either we answer Question 1 incorrectly or we answer Question 2 incorrectly
P(X=100) = We answer Question 1 correctly and answer Question 2 incorrectly
P(X=200) = We answer Question 2 correctly and answer Question 1 incorrectly
P(X=300) = We answer Question 1 and then Question 2 correctly in that order or
We answer Question 2 and then Question 1 correctly in that order
But if we sum P(X=0) + P(X=100) + P(X= 200) + P(X=300) = 2
Where I am getting wrong?