1a) A certain typing agency employs two typists. The average number of errors per article is 3.53.5 when typed by the first typist and 1.81.8 when typed by the second. If your article is equally likely to be typed by either typist, find the probability that it will have no errors.

1b) Flaws in a carpet tend to occur randomly and independently at a rate of one every 250 square feet. What is the probability that a carpet that is 7 feet by 12 feet contains no flaws?

Probability =