Răspuns:
4/11 (aprox 36%)
Explicație pas cu pas:
M = {x ∈ N | x < 21}
M = {0, 1, 2, 3, 4, ...., 20, 21}
card M = 22 elemente
⇒ nr cazuri posibile = 22
x = nr prim ⇒ x ∈ {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31 ...}
dar x < 21
⇒ x ∈ {2, 3, 5, 7, 11, 13, 17, 19}
card = 8 elemente
⇒ nr cazuri favorabile = 8
probabilitate = nr cazuri favorabile : nr cazuri posibile
probabilitate = 8/22
= 4/11
