In how many ways can a person enter a room that has three doors and leave it by
(a) a different door?
(b) any door?

how many four-digit numbers can you form from the numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9
(a) if you use each digit only once?
(b) if you can repeat each digit?

a man has four coats and seven pairs of trousers. how many different outfits can he make if he can wear any coat with any pair of trousers?

you toss two coins. in how many ways can they fall?

you toss three coins. in how many ways can they fall?

you throw two dice. in how many ways can they fall?

if 10 athletes run a race, in how many ways might the first, second, and third prizes be awarded?

to how many patrons could a telephone company furnish numbers having five digits, the first digit not being zero?

and can you explain you