Unnamed

Devices can fail by wear-out (a gradual change of properties with time) or by
sudden failure (where the device just stops working without warning). If the
MTTF is expected to be >N for a device, what is the minimum number of devices
that would have on life test with no failures for (1) one week (2) one month
(3) one year to claim with a confidence level of gamma (with N and gamma as
given in the web page) that the MTTF is > N years. For this question, ignore
wear-out aging.