I don't Understand these questions:

Compare groups 2 and 3 using a planned comparison and a nondirectional H_{1 .}

What are thedffor a planned comparison?

With a planned comparison using an ? = 0.05, what is the appropriate t_crit?This is the original problem:

An investigator conducts an experiment involving the effects of three levels of a drug on memory.Subjects are randomly assigned to one of three conditions.A different drug level is administered in each condition.Memory is measured 10 minutes after each subject receives the drug.The following scores are recorded.The higher the score, the better the memory.

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