Hello,

I need help in solving part i) of the question using the normal distribution table (not a calculator or excel formula). Assuming mean=15 and standard deviation=4, how can i find the probability of minutes between 20-30 and more than 30 for both options ( I get stuck after getting a z value of 3.75 which is not within the normal distribution table.

A business consultant requires assistance in deciding between two mobile phone options. These are shown below. Option 02 Option V1 Rental per month E14 E180 Insurance per month E2.50 E6.00 Itemised billing per month Free $1.50 Call time included in rental None 2000 minutes of calls package per month Additional call charges: Less than E0.35 E0.30 10 minutes 10 to 20 10.25 E0.20 minutes 20 to 30 E0. 15 E0. 15 minutes More than E0.05 E0. 10 30 minutes The business consultant estimates that his typical call time is 15 minutes and rarely would a call be shorter than 3 minutes or longer than 27. Typically he makes about 350 calls per month. (i) Assuming the distribution of call times is Normal, write down the mean and standard deviation of your model and hence estimate the percentage of calls the business consultant is likely to make in the four call bands. (5 marks) (ii) Calculate the expected costs per month for each of the two options and explain which one you would recommend. State any assumptions you make. (10 marks)