Question 618086
a.) treat T1/T2 as a single entity, so you are working with 5 tests instead of 6
___ should be 5!


b.) similar argument
___ now two entities, T1/T2 and T2/T1
___ so 2 * 5! not allowed
___ 6! - (2 * 5!)



6! is the number of ways of arranging 6 things in order
___ when T1 and and T2 become a single thing, then there are 5 things to arrange in order; so 5!
___ in b, there are two arrangements of T1 and T2; so 5! is subtracted twice from the total possible arrangements