Ответ: [tex]a) \frac{C_5^1*C_7^2}{C_{12}^3}= \frac{5*21}{220}= \frac{105}{220}=\frac{21}{44}=0,48\\\\b)\frac{C_5^1*C_7^2+C_5^2*C_7^1+C_5^3}{C_{12}^3}= \frac{105+70+10}{220}= \frac{185}{220}=0,84 [/tex]