[tex]1.3kg - 100\% \\ x - 7\% \\ \\ x = \frac{1.3 \times 7}{100} = \frac{9.1}{100} = 0.091kg - sol[/tex]
[tex]1.3 - 100\% \\ x - 4\% \\ \\ x = \frac{1.3 \times 4}{100} = \frac{5.2}{100} = 0.052kg[/tex]
Ile należy dodać?
[tex]0.091 - 0.052 = 0.039kg[/tex]
[tex]0.039kg = \boxed{39g}[/tex]
