(-20)(6)
-120
Just multiply those numbers together I believe
I've attached the correct image to this answer, just in case they're scrambled.
A can do 1 job in 10 min. means 1/10 job per min.
B can do 1/15 job per min.
together A&B can do 1/10+1/15 =1/6 job per min.
1/6 job they spend 1 min
1 spend 1x1/(1/6) = 6 min
The first choice is correct
Answer:

The mean of the distribution is 0.25.
The variance of the distribution is of 0.6875.
Step-by-step explanation:
Probability density function:
For it to be a probability function, the sum of the probabilities must be 1. The probabilities are 3c, 3c and 6c, so:



So the probability distribution is:



Mean:
Sum of each outcome multiplied by its probability. So

The mean of the distribution is 0.25.
Variance:
Sum of the difference squared between each value and the mean, multiplied by its probability. So

The variance of the distribution is of 0.6875.