In how many ways can 4 people sit next to each other in a movie theater row? [? ] question 4 options:

Any of the 4 people can take the first seat
since it gets occupied by one person , the next seat can be occupied by any of the remaining 3
similarly, the next one has 2 possibilities and the last seat can only be occupied by the man who is left

so by the principal of multiplication, no. of ways equals 4! = 4×3×2×1 = 24 ways