A purchasing unit for a state government has found that 60% of the winning bids for office-cleaning contracts come from regular bidders, 30% from occasional bidders and 10% from first-time bidders. The services provided by successful bidders are rated satisfactory or unsatisfactory after one year on the job. Experience indicates that 90% of the jobs done by regular bidders are satisfactory, as are 80% of the jobs done by occasional bidders and 60% of the jobs done by first-time bidders. a. What is the probability that a job will be done by a first-tim