Answer:
Mean = 1.57
Variance=0.31
Step-by-step explanation:
To calculate the mean and the variance of the number of successful surgeries (X), we first have to enumerate the possible outcomes:
1) Both surgeries are successful (X=2).
2) Left knee unsuccessful and right knee successful (X=1).
3) Right knee unsuccessful and left knee successful (X=1).
4) Both surgeries are unsuccessful (X=0).
Then, the mean can be calculated as the expected value:
The variance can be calculated as: