Question

There are six entrances to a haunted House. If you do not exit the same way you entered, how many different ways can you enter and exit the house?

A.) 20

B.) 25

C.) 30

D.) 36

Answer 1

There are 6 ways to enter and 5 ways to leave once you pick a specific door to enter (in which you cannot re-use to exit). So overall there are 6*5 = 30 different permutations to pick from

Answer: Choice C) 30

Note: you can use the nPr formula with n = 6 and r = 2 to get the same answer
Alternatively, you can use a probability tree to map out all the possibilities though such a tree with 30 branches may take a while to draw out 

Answer 2

C would be the right answer