ST 2-True or False: For a t distribution with 12 degrees

Question
4. a True or False: For a t distribution with 12 degrees of freedom, the area between 2.6810 and 2.1788 is 0.970.

4.b True or False: For a t distribution with 12 degrees of freedom, the area between -2.6810 and 2.1788 is 0.970.

4c. Mark wants to evaluate the GPAs of current ABC undergraduate students. He has received a list of all current students from the registrar and wants to take a probability based sample from this list. If Mark wants to ensure that his final sample is comprised of 30% freshman, 25% sophomores, 25% juniors, and 20% seniors, which sampling method would be most appropriate?

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