Of 400 employees at a company, 25% work in production, 40% work in sales and marketing, and

Question:

Of 400 employees at a company, 25% work in production, 40% work in sales and marketing, and 35% work in new product development. As part of a security awareness training program, the group overseeing implementation of the program will randomly choose a sample of 20 employees to begin the training; the percentages of workers from each department in the sample are to align with the percentages throughout the company.
a. What type of sampling could be used to achieve this goal?
b. Explain how to carry out the sampling using a table of random digits.