In a set of ordered pairs for which the x-coordinates increase by a constant amount, which identifies the set as representing exponential decay?
a. the y-coordinates decrease by a constant amount
b. the y-coordinates by a constant negative factor
c. the coordinated decrease by a constant positive factor between 0 and 1
d. the coordinates are always negative and decreasing

The weekly amount spent by a company for travel has an approximately normal distribution with mean = $550 and standard deviation = $40. a) what is the probability that the actual weekly expense will exceed $570 for more than 20 weeks during the next year? (note: one year = 52 weeks) b) what is the probability that actual weekly expenses exceed $580 for 10 or more, but 16 or fewer weeks during the next year?