\[\boxed{\text{778\ (778).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ C_{10}^{1} = \frac{10!}{1! \cdot 9!} = 10\ способов.\]
\[\textbf{б)}\ C_{10}^{3} = \frac{10!}{3! \cdot 7!} = \frac{8 \cdot 9 \cdot 10}{6} =\]
\[= 120\ способов.\]
\[\textbf{в)}\ C_{10}^{2} = \frac{10!}{2! \cdot 8!} = \frac{9 \cdot 10}{2} =\]
\[= 45\ способов.\]