\[\boxed{\text{872\ (872).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[При\ бросании\ трех\ кубиков\ \]
\[возможно\ выпадение\]
\[6 \cdot 6 \cdot 6 = 216\ вариантов.\]
\[\textbf{а)}\ 1 + 1 + 1 = 3 \Longrightarrow один\ \]
\[вариант,\ что\ выпадет\ в\ \]
\[сумме\ 3;\]
\[P(A) = \frac{1}{216}.\]
\[\textbf{б)}\ 4 = 1 + 1 + 2;\]
\[4 = 1 + 2 + 1;\]
\[4 = 2 + 1 + 1 \Longrightarrow 3\ варианта;\]
\[P(B) = \frac{3}{216} = \frac{1}{72}.\]
\[\textbf{в)}\ 5 = 1 + 2 + 2;\ \ \]
\[5 = 2 + 2 + 1;\ \ 5 = 2 + 1 + 2;\ \ \ \]
\[5 = 1 + 1 + 3;\ \ \ 5 = 1 + 3 + 1;\ \]
\[5 = 3 + 1 + 1 \Longrightarrow 6\ вариантов;\]
\[P(C) = \frac{6}{216} = \frac{1}{36};\]
\[\textbf{г)}\ 7 = 2 + 2 + 3;\ \ \ 7 = 2 + 3 + 2;\ \ \ \]
\[7 = 3 + 2 + 2;\ \ 7 = 1 + 1 + 5;\]
\[7 = 1 + 5 + 1;\ \ 7 = 5 + 1 + 1;\ \ \ \]
\[7 = 1 + 2 + 4;\ \ 7 = 1 + 4 + 2;\]
\[7 = 2 + 4 + 1;\ \ \ 7 = 4 + 2 + 1;\ \ \]
\[7 = 4 + 1 + 2;\ \ 7 = 2 + 1 + 4;\ \]
\[7 = 1 + 3 + 3;\ \ \ 7 = 3 + 3 + 1;\ \ \]
\[7 = 3 + 1 + 3\]
\[\Longrightarrow 15\ вариантов.\]
\[P(D) = \frac{15}{216} = \frac{5}{72}.\]