a. there are no restrictions? 10! = 10*9*8*7*6*5*4*3*2*1 = 3628800 ways. b. each couple must be seated together?= 120*32 = 3840 ways (120 permutations for 5 objects, each of which can be in one of the two states: (h,w) or (w,h), where "h" stands for husband and "w" stands for wife. c. each husband must be seated to the left of his wife? 5! = 5*4*3*2*1 = 120 ways.