a)
[tex]\it m_{a.p.}=\dfrac{4\cdot\sqrt{20}+8\sqrt5+3\sqrt{45}}{4+8+3}=\dfrac{4\sqrt{4\cdot5}+8\sqrt5+3\sqrt{9\cdot5}}{15}=\dfrac{8\sqrt5+8\sqrt5+9\sqrt5}{15}=\\ \\ \\ =\dfrac{25\sqrt5^{(5}}{15}=\dfrac{5\sqrt5}{3}[/tex]
b)
[tex]\it m_{a.p.}=\dfrac{14\cdot\dfrac{2}{7}+10\cdot\dfrac{3}{5}+12\cdot\dfrac{1}{6}}{14+10+12}=\dfrac{2\cdot2+2\cdot3+2\cdot1}{36}=\dfrac{4+6+2}{36}=\\ \\ \\ =\dfrac{\ \ 12^{(12}}{36}=\dfrac{1}{3}[/tex]
