How many pints of a 30% sugar solution must be added to a 5 pint of a 5% sugar solution to obtain a 20% sugar solution?

You must add 7.5 pt of the 30 % sugar to the 5 % sugar to get a 20 % solution.

You can use a modified dilution formula to calculate the volume of 30 % sugar.

V_1*C_1 + V_2*C_2 = V_3*C_3

Let the volume of 30 % sugar = x pt. Then the volume of the final 20 % sugar = (5 + x) pt

(x pt*30 % sugar) + (5 pt*5 % sugar) = (x + 5) pt * 20 % sugar

30x + 25 = 20x + 100

10x = 75

x = 75/10 = 7.5