Npontos = 1e7;
X = rand(1,Npontos);
Y = 2*rand(1,Npontos);
Z = X+Y;ax= gca;
ax.FontSize = 20;

subplot(311); hX = histogram(X,'Normalization','pdf');
xlabel('x'); ylabel('f_X(x)'); grid; title('X --> U[0,1]');
xlim([0 3]);
ax= gca;
ax.FontSize = 20;

subplot(312); hY = histogram(Y,'Normalization','pdf');
xlabel('Y'); ylabel('f_Y(y)'); grid; title('Y --> U[0,2]');
xlim([0 3]);
ax= gca;
ax.FontSize = 20;

subplot(313); hZ = histogram(Z,'Normalization','pdf');
xlabel('Z'); ylabel('f_Z(z)'); grid; title('Z = X+Y');
xlim([0 3]);
ax= gca;
ax.FontSize = 16;