(a) Let x be the amount of red potion that must be added to 500 mL of blue potion. The total volume of the mixture will be x+500 mL. The total amount of magical syrup in the mixture will be 0.6x+0.3(500)=0.6x+150 mL. We want the mixture to be 40% magical syrup, so we have the equation:
0.6x+150 = 0.4(x+500)
1.2x = 200
x = 166.67 mL
Therefore, 166.67 mL of red potion must be added to 500 mL of blue potion in order to produce a potion that is 40% magical syrup by volume.
(b) Let x be the amount of red potion and y be the amount of blue potion that are combined to produce 100 mL of a potion that is 54% magical syrup by volume. The total volume of the mixture will be x+y mL. The total amount of magical syrup in the mixture will be 0.6x+0.3y mL. We want the mixture to be 54% magical syrup, so we have the equation:
0.6x+0.3y = 0.54(x+y)
0.06x = 0.18y
x = 3y
Since we want the total volume of the mixture to be 100 mL, we have the equation:
x+y = 100
Substituting x=3y into the second equation, we get:
3y+y = 100
4y = 100
y = 25
Since x=3y, we have x=3(25)=75.
(c) I'll leave you to think about this one.