1. The wearout of a machine part is normally distributed with 90 percent of the failures occurring between 200 and 270 hr of use (i.e., 5 % below 200 hr and 5% above 270 hr.)

Find the MTTF and the standard deviation of failure times.

What is the reliability if the part is to be used for 210 hr and then replaced?

Determine the design life if no more than 1 percent probability of failure prior to the replacement to be tolerated?

Compute the reliability for a 10-hr use if the part has been operating for 200 hr (i.e., find the conditional reliability).