The mathematics department wishes to form a sample from each of 10 courses offered. They randomly select three individuals from each course and include them in the 30-person sample. Which of the following methods was used to select the probability sample?(A) Random
(B) Systematic
(C) Stratified
(D) Cluster
(E) Simple random

C) Stratified

Step-by-step explanation:

We know that the mathematics department wishes to form a sample from each of 10 courses offered.They randomly select three individuals from each course and include them in the 30-person sample.

We conclude that was used a stratified sample. That s a stratified sample because the population was first divided into 10 sections and then randomly select three individuals.

C) Stratified

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.