Question

Assume that there are 8 rats in the cage: 6 trained and 2 untrained. A rat is removed from the cage and it is noted whether or not it is trained. It is then placed in a different cage. 4 more rats are removed and treated the same way. How many outcomes are possible for this experiment?

Answer 1

First remove:

Probability of removing a trained rat is 6/8

Probability of removing untrained rat is 2/8

Outcome is 6/8 + 2/8 = 1

Second remove:

Probability of picking a trained rat is 5/7

Probability of picking untrained rat is 1/7

Outcome is 6/7

Third remove:

Outcome is 1 (Since you can only remove a trained rat)

Forth remove:

Outcome is 1 (Since you can only remove a trained rat)

Fifth remove:

Outcome is 1 (Since you can only remove a trained rat)

Total outcome = 1 + 6/7 + 1 + 1 + 1 = 34/7 = 4(6/7)