Răspuns:
Explicație pas cu pas:
{0,1,2,3,4,5,6,7}
[tex]C_{7}^{0}=\dfrac{7!}{0!*(7-0)!}=\dfrac{7!}{1*7!}=1,~~nu~e~prim\\C_{7}^{1}=\dfrac{7!}{1!*(7-1)!}=\dfrac{7!}{1*6!}=\dfrac{6!*7}{1*6!}=7,~~este~prim\\C_{7}^{2}=\dfrac{7!}{2!*(7-2)!}=\dfrac{7!}{2*5!}=\dfrac{5!*6*7}{2*5!}=21,~nu~este~prim\\C_{7}^{3}=\dfrac{7!}{3!*(7-3)!}=\dfrac{7!}{3!*4!}=\dfrac{4!*5*6*7}{6*4!}=35,~nu~este~prim\\C_{7}^{4}=C_{7}^{7-4}=C_{7}^{3}=35,~nu~este~prim\\C_{7}^{5}=C_{7}^{7-5}=C_{7}^{2}=21,~nu~este~prim\\C_{7}^{6}=C_{7}^{7-6}=C_{7}^{1}=7,~~este~prim\\[/tex]
[tex]C_{7}^{7}=C_{7}^{7-7}=C_{7}^{0}=1,~nu~este~prim[/tex]
nr posibil de cazuri, n=8
nr de cazuri favorabile, m=2
P=m/n=2/8=1/4.
