Final answer:
The preferred way for a project manager to calculate probabilities of similar risks for current projects is by using data from past projects.
Step-by-step explanation:
The question is discussing the preferred way for a project manager to calculate probabilities of similar risks for current projects. The answer lies in using data from past projects to inform the estimation of probabilities. By analyzing historical data, project managers can identify trends, patterns, and potential risks that are likely to occur in current projects. This approach allows project managers to make more informed decisions and better estimate the probabilities of risks in their current projects.