\[\boxed{\mathbf{3.34}}\]
\[1)\ 40\ :1200 \cdot 100 = \frac{4000}{1200} =\]
\[= \frac{40}{12} = \frac{10}{3} = 3\frac{1}{3}\% -\]
\[содержание\ соли\ в\ растворе.\]
\[2)\ 1200 + 800 = 2000\ (г) -\]
\[воды\ стало.\]
\[3)\ 40\ :2000 = \frac{40}{2000} = \frac{4}{200} =\]
\[= \frac{2}{100} = 0,02\ или\ 2\% - соли\ \]
\[стало\ в\ растворе.\]
\[Ответ:3\frac{1}{3}\%;2\%.\]