Suppose that the amount of time that a lightbulb works before burning itself out is exponentially distributed with mean ten hours. Suppose that a person enters a room in which a lightbulb is burning....

Suppose that the amount of time that a lightbulb works before burning itself out is exponentially distributed with mean ten hours. Suppose that a person enters a room in which a lightbulb is burning. If this person desires to work for five hours, then what is the probability that she will be able to complete her work without the bulb burning out? What can be said about this probability when the distribution is not exponential?