Defective concrete on a construction project can be caused by either poor aggregates or poor workmanship (such as selection and grading of material, pouring, curing) or both. The quality of aggregates is also affected by the quality of workmanship and vice versa. On a given project, the probability of poor aggregates is 0.20. The probability of poor workmanship if the aggregates are poor is 0.30. The probability of poor aggregates if there is poor workmanship is 0.15.

(a) What is the probability of poor workmanship on the project?