I have to give it in N(mean, standard deviation).A manufacturer says that not only will 90% of their copiers last at least 36 months, 65% will last at least 42 months. What Normal model parameters is that manufacturer claiming? Show your work.
I don't even know where to start . Maybe I have to compare the percentages and the months to find a standard deviation first but I don't know how to do it.
I'm also confused about the percentages. I understand that it makes logical sense that more copiers would last 36 months than 42 months, but the bell shaped curve works backwards then, since the scale is from lowest to highest and the percentage (based on the z-score) is likewise.