\[\boxed{\mathbf{4.95}}\]
\[\textbf{а)}\ 70\ :5 = 14 + 2 = 16 \cdot 4 =\]
\[= 64 - 64 = 0\ :11 = 0\ \]
\[\textbf{б)}\ 48\ :4 = 12 - 2 = 10 \cdot 9 =\]
\[= 90\ :45 = 2 + 18 = 20\]
\[\textbf{в)}\ 15 \cdot 6 = 90 - 21 = 69\ :23 =\]
\[= 3 + 49 = 52\ :13 = 4\]
\[\textbf{г)}\ 17 \cdot 3 = 51 + 49 = 100\ :25 =\]
\[= 4 + 38 = 42\ :14 = 3\ \]
\[\textbf{д)}\ 75\ :25 = 3 \cdot 19 = 57 + 8 =\]
\[= 65\ :13 = 5 \cdot 20 = 100\]