please solve this using excel formulas

In an effort to check the quality of their cell phones, a manufacturing manager decides to take a random sample of 10 cell phones from yesterday's production run, which produced cell phones with serial numbers ranging (according to when they were produced) from 43005000 to 43005999. The manager noticed that the number of faulty cell phones in the production run of cell phones is usually small and that the quality of one day's run seems to have no bearing on the next day. The cell phone manufacturer wants to model the time between faulty phones. The mean number of defective cell phones is 1.7 per day, a. What is the mean time between failures? b. What would the probability be that the time to the next failure will be between 1 and 3 days? A bank makes loans to small businesses and on average 4.1% of them default on their loans within five years. The bank makes provision for these losses when it makes its financial plans. The Vice President in charge of small business loans thinks that the default rate may be going down and gives you a random sample of 250 recent loans of which 6 defaulted within five years. What advice do you give to the Vice President