This is a good way to think of it:
* For the first person to be allocated into a room, there are 4 possible rooms to choose from.
* For the second person to be allocated into a room, there are 4 possible rooms to choose from.
* For the third person to be allocated into a room, there are 4 possible rooms to choose from.
* For the fourth person to be allocated into a room, there are 4 possible rooms to choose from.
.'. number of ways = 4.4.4.4 = 44 or 256.