If 5 subjects are selected from the 9 that are​ available, and the 5 selected subjects are all treated at the same​ time, how many different treatment groups are​ possible?

Question

A clinical test on humans of a new drug is normally done in three phases. Phase I is conducted with a relatively small number of healthy volunteers. For​ example, a phase I test of a specific drug involved only 5 subjects. Assume that we want to treat 5 healthy humans with this new drug and we have 9 suitable volunteers available.

If 5 subjects are selected from the 9 that are​ available, and the 5 selected subjects are all treated at the same​ time, how many different treatment groups are​ possible?

There are __ nothing different treatment groups possible.

Answer 1

Order does not make a difference. This is a combination.

₉C₅ = ?