The Canadian mining company Barrick Gold operates the Donlin Creek mining project in the Yukon–Kuskokwin region, today providing stable employment with 90% First Nations people as employees and supervisors. When another mining company started the project in 1996, employment conditions were much worse. There was a 50% probability of employees failing drug screening tests and hence being fired. Of those who passed the test, there was a 70% chance that they would resign from their jobs. What was the probability that an employee would leave employment either as a result of failing the drug test or as a result of resignation? State your reasoning and assumptions clearly.