Răspuns:
Explicație pas cu pas:
a. 2
b. (a,b,y), (a,y,b), (b,a,y), (b,y,a), (y,a,b), (y,b,a)
c. (4,5), (5,4)
d. (a,b,c,d), (a,b,d,c), (a,c,d,b), (a,c,b,d), (a,d,b,c), (a,d,c,b)
(b,a,c,d), (b,a,d,c), (b,c,a,d), (b,c,d,a), (b,d,a,c), (b,d,c,a)
(c,a,b,d), (c,a,d,b), (c,b,a,d), (c,b,d,a), (c,d,a,b), (c,d,b,a)
(d,a,b,c), (d,a,c,b), (d,b,a,c), (d,b,c,a), (d,c,a,b), (d,c,b,a)