You would like to ensure that your sample is representative of the racial mix seen in your population of interest. The population is 50% Asian, 20% African American, 20% Caucasian, and 10% other. You need a sample of 500 subjects. You program your statistical software to select randomly 250 Asian subjects from your population, 100 African American subjects, 100 Caucasian subjects, and 50 subjects identified as other.

a.) What type of sample is this?

b.) is it probability or non probability sample?