An experiment compares four different mixtures of the components oxidizer, binder, and fuel used in the manufacturing of rocket propellant. The four mixtures under test, corresponding to settings of the mixture proportions for oxide, are shown here.

To compare the four mixtures, five different samples of propellant are prepared from each mixture and readied for testing. Each of five investigators is randomly assigned one sample of each of the four mixtures and asked to measure the propellant thrust. These data are summarized next.

a. Identify the blocks and treatments for this experimental design.
b. Indicate the method of randomization.
c. Why would this design be preferable to a completely randomized design?

Mixture Oxidizer Binder Fuel Investigator Mixture 2.362 2658 2,650 6 2,640 2,653 2.340 2355 2,350 2,348 2,449 2458 2.43.2 2.403 2410 2,418 2,437 2,445 2,397 2,405