Answer: 81.25 mL Why? Total amount of millilitres: 125 mL Let x represent the millilitres of acid. Let a represent the amount of acid in the 50 mL solution. Let b represent the amount of acid in the 75 mL solution. This means that x = 125 - (a + b) So, a = 0.2*50 a = 10 So, b = 0.45*75 b = 33.75 Plug it into our equation; x = 125 - (a + b) x = 125 - (10 + 33.75) x = 125 - 43.75 x = 81.25 Therefore, 81.25 mL of the 125 mL mixture is acid. Alternate solution: Let x represent the millilitres of acid. Let a represent the number of millilitres in the mixture. Let b represent the percentage of acid in the mixture. This means that x = b*a So, a = 50 + 75 a = 125 So, b = 0.2 + 0.45 b = 0.65 Plug it into our equation; x = b*a x = 0.65*125 x = 81.25 Therefore, 81.25 mL of the 125 mL mixture is acid.
