How do I solve Question #7, especially 7B in finding the standard deviation and what would the excel formula be.
1. Complete the table below (3 points) Hints: Note that probability is just the proportion or relative frequency. Number of Calls per Frequency month per User (X) (Number of Users) Probability: P(X=x1) 510 0.204 457 0.1828 366 0.1464 332 0.1328 274 0.1096 211 0.0844 152 0.0608 104 0.0416 94 0376 TOTAL 2500 2. What is the probability that a user would make at least 55 calls per month? (2 points) Use an Excel formula to get your answer and place it in cell C40. 0.334 3. What is the average number of calls that the telephone company can expect its customers to make each month when they sign up for the plan? (1 point) Hint: Would the SUMPRODUCT function be useful here? 48.456 4. Cellular phone service costs to the company are, on average, $0.35 per call plus a fixed cost of $15 per user per month. Let C be the random variable denoting total cost per user per month and X denote the number of calls per month per user. Show the relationship between C and X by entering on the line below the equation which expresses C in terms of X. (1 point C= .35x + 15 5. What is the expected value of the monthly amount a customer pays to Tellucell? Make sure your formula uses the data referenced in the cells below and your answer to question 3. above. (1 point) Hint: You might find the sheet Transformation of a R.V. taken from the lecture slides for Chapter 6 $ 31.96 Price per call = $ 0.35 Fixed cost/month = $ 15.00 6. If the standard deviation of the random variable, X, is o(X) = 11.42 , what would be the standard deviation of the random variable, C? (2 points) 4.00 7. Consider the following two phone plans: Plan 1: Each customer pays 240.00 for a new phone and is charged a flat rate = c $ 55.00 per month. Plan 2: Each customer pays 500.00 for a new phone and is charged $ 0.50 per call plus a flat rate of $ 20.00 per month. from its customers over two Let R1 and R2 be the random variables denoting the per user revenue the company gets from its customers over two years. A. In the cells below, enter formulas that compute the expected values of R1 and R2. (2 points) E(R1) = $ 1,560.00 E(R2) = $ 1,561.47 B. In the cells below, enter the standard deviations of R1 and R2? (4 points) SD (R1) = SD(R2) = C. Which plan is more enticing to the company? Justify your answer in one line below. (1 point)
