# Thread: Expected value and covariance

1. ## Expected value and covariance

I was able to solve other problems relating to expected portfolio returns however I am stuck with solving this simple problem.

The sign on the lift in a building states ‘Maximum capacity 1120kg or 16 persons’. A statistics practitioner wonders what the probability is that 16 people would weigh more than 1120kg. If the weights of the people who use the lift are normally distributed with a mean of 68kg and a standard deviation of 8kg, what is the probability that the statistics practitioner seeks?

[Hint: If you are using the variance equation
[Var(X+Y) = sigma x+y ^2 = sigma x^2 + sigma y^2 + 2sigma xy]
assume the covariance to be zero because people’s weights are independent. and covariance is sigma xy]

2. Originally Posted by crustyv
I was able to solve other problems relating to expected portfolio returns however I am stuck with solving this simple problem.

The sign on the lift in a building states ‘Maximum capacity 1120kg or 16 persons’. A statistics practitioner wonders what the probability is that 16 people would weigh more than 1120kg. If the weights of the people who use the lift are normally distributed with a mean of 68kg and a standard deviation of 8kg, what is the probability that the statistics practitioner seeks?

[Hint: If you are using the variance equation
[Var(X+Y) = sigma x+y ^2 = sigma x^2 + sigma y^2 + 2sigma xy]
assume the covariance to be zero because people’s weights are independent. and covariance is sigma xy]
See here: http://www.mathhelpforum.com/math-he...gent-help.html