Expected Value- Random variables - PowerPoint PPT Presentation

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Expected Value- Random variables

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  1. Expected Value- Random variables Def. A randomvariable, X, is a numerical measure of the outcomes of an experiment

  2. Example: • Experiment- Two cards randomly selected Let X be the number of diamonds selected

  3. Events can be described in terms of random variables Example: • is the event that exactly one diamond is selected • is the event that at most one diamond is selected

  4. Probabilities of events can be stated as probabilities of the corresponding values of X

  5. Example:

  6. In general, is the probability that X takes on the value x is the probability that X takes on a value that is less than or equal to x

  7. Suppose that X can only assume the values x1, x2, ... xn. Then

  8. Def. The mean (or expectedvalue) of X gives the value that we would expect to observe on average in a large number of repetitions of the experiment

  9. Important • Concept of Expected value describe the expected monetary return of experiment Sum of the values, weighted by their respected probabilities

  10. Example (Exercise 13): An investment in Project A will result in a loss of $26,000 with probability 0.30, break even with probability 0.50, or result in a profit of $68,000 with probability 0.20. An investment in Project B will result in a loss of $71,000 with probability 0.20, break even with probability 0.65, or result in a profit of $143,000 with probability 0.15. Which investment is better?

  11. Tools to calculate E(X)-Project A • Random Variable (X)- The amount of money received from the investment in Project A • X can assume only x1 ,x2 ,x3 X= x1 is the event that we have Loss X= x2 is the event that we are breaking even X= x3 is the event that we have a Profit • x1=$-26,000 • x2=$0 • x3=$68,000 • P(X= x1)=0.3 • P(X= x2)= 0.5 • P(X= x3)= 0.2

  12. Tools to calculate E(X)-Project B • Random Variable (X)- The amount of money received from the investment in Project B • X can assume only x1 ,x2 ,x3 X= x1 is the event that we have Loss X= x2 is the event that we are breaking even X= x3 is the event that we have a Profit • x1=$-71,000 • x2=$0 • x3=$143,000 • P(X= x1)=0.2 • P(X= x2)= 0.65 • P(X= x3)= 0.15

  13. Focus on the Project • How can Expected value help us with the decision on whether or not to attempt a loan workout? • Recall: Events S- An attempted workout is a Success F- An attempted workout is a Failure

  14. Tools to calculate E(X) • Random Variable (X)- The amount of money Acadia receives from a future loan workout attempt • X can assume only Full Value Default Value x1=$ 4,000,000 x2=$ 250,000

  15. The sheet Expected Value in the Excel file Loan Focus.xls performs the following computation for the expected value of X. • Using Expected value formula

  16. Decision? Recall • Bank Forecloses a loan if Benefits of Foreclosure > Benefits of Workout • Bank enters a Loan Workout if Expected Value Workout > Expected Value Foreclose

  17. Since the expected value of a work out is $1,991,000 and the “expected value” of foreclosing is a guaranteed $2,100,000, it might seem that Acadia Bank should foreclose on John Sanders’ loan.