Let x be the amount of neutral solution we need to add.
Since we have 40 fl of 5% local anesthesia solution, we have [tex](40)( \frac{5}{100} )=2[/tex] fl of pure anesthesia.
After adding neutral solution, our new volume will be [tex]40+x[/tex]. Remember that the concentration of the anesthesia after adding neutral solution should be 5%=0.05, and since the volume of the pure anesthesia won't change, we can relate all the values with the equation:
[tex] \frac{2}{40+x} =0.04[/tex]
[tex]40+x= \frac{2}{0.04} [/tex]
[tex]40+x=50[/tex]
[tex]x=10[/tex]
We can conclude that we will need to add 10 fl of neutral solution to our 40 fl of 5% anesthesia solution to get 50 fl of 4% anesthesia solution.
