52 i believe.
42 + 45 + 58 + 63 = 208
208 / 4 = 52
Answer: The correr solution is 
Step-by-step explanation:
Since the steps in Lin's solution are not shown, we are not able to find her erros. However, we can solve it step by step and find the correct result:

Firstly, in the left part of the equation we have to multiply
by the numbers inside the parenthesis; and in the right side we have to solve first what is inside the parenthesis:

Adding similar terms in the left side and multiplying
by the number inside the parenthesis in the right side:

Isolating
:
This is the correct solution
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:

The figure below shows a diagram of this problem. First of all we graph the hemisphere. This one has a radius equal to 1. Given that z ≤ 0 a sphere will be valid only in the negative z-axis, that is, we will get a half of a sphere that is the hemisphere shown in the figure. We know that this hemisphere is oriented by the inward normal pointing to the origin, then we have a Differential Surface Vector called
N, using the Right-hand rule <span>the boundary orientation is </span>counterclockwise.
Therefore, the answer above
False