Bonsoir Elenapancho
1) Arbre : voir pièce jointe
[tex]2)\ a)\ p(R;V)=\dfrac{3}{7}\times\dfrac{3}{4}\\\boxed{p(R;V)=\dfrac{9}{28}}\\\\\\b)\ p(V;R)=\dfrac{4}{7}\times\dfrac{1}{4}\\\boxed{p(V;R)=\dfrac{1}{7}}\\\\\\c)\ p((R;R)\ ou\ (V;V))=\dfrac{3}{7}\times\dfrac{1}{4}+\dfrac{4}{7}\times\dfrac{3}{4}\\\\p((R;R)\ ou\ (V;V))=\dfrac{3}{28}+\dfrac{12}{28}[/tex]
[tex]\\\boxed{p((R;R)\ ou\ (V;V))=\dfrac{15}{28}}[/tex]