Answer:
1) UUUTU
2) 20 possible outcomes.
Step-by-step explanation:
We have 3 trained rats (T) and 3 untrained cats (U).
1) Which of the following is not a valid outcome?
a) UUUTU is not a valid outcome because we can only have 3 U's at most.
2) How many outcomes are possible for this experiment?
We have to choose 5 rats, at the end we're going to have either 3 trained and 2 untrained (TTTUU) or 3 untrained and 2 trained (TTUUU)
To help with this, we can make a decision tree, which can be observed below.
From the image we can tell that there are 20 possible outcomes for this experiment.