The lives of parts are often expressed as the number of cycles of operation that a specified percentage of a population will exceed before experiencing failure. The symbol L Page 38 is used to designate this definition of life. Thus, we can speak of L10 life as the number of cycles to failure exceeded by 90 percent of a population of parts. Given a normal distribution model, with a mean L= 122.9 of kilocycles and standard deviation of sL = 30.3 kilocycles, estimate the corresponding L10 life.

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.