a) Statistics are collecting, organizing, summarizing and presenting a set of data.
b) Inferential statistics is the learn of a sample that enables us to make estimates about the population from which the sample is drawn.
c) A "thickness of a sheet" of sheet metal used in manufacturing process is an example of a quantitative variable.
d) There are 2000 students in a school. Randomly, 300 were chosen for an option survey.The 300 students can be organized as the population.