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:

Answer:
t=-8
Step-by-step explanation:
-5t-2(5t+10t)=100
-2 x 5t=-10t
-2 x 10 = -20
-5t-10t-20=100
combine terms and add 20
-15t=120
divide by -15
t=-8
Answer: Samson is correct
Step-by-step explanation: OK MODS LOOK I EXPLAINED IT GO BULLY SOMEONE ELSE 
It’s the first one. -9a^3b^2
-69 is the answer i think