Two bottles contain acid and water in ratio 2 : 3 and 1 : 2 respectively. These are mixed in ratio 1 : 3. What is ratio of acid and water in new mixture = ?

Let 1 bottle of acid is 30litre and consider the first bottle as A and second bottle as B.
Ratio of Acid and water in bottle A = 2 : 3
Volume of Acid in bottle A = $$\frac{2}{5} \times 30 = 12$$
Volume of Water in bottle A = $$\frac{3}{5} \times 30 = 18$$

Ratio of Acid and water in bottle A = 1 : 2
Volume of Acid in bottle A = $$\frac{1}{3} \times 30 = 10$$
Volume of Water in bottle A = $$\frac{2}{3} \times 30 = 20$$

Now 1 bottle of A and 3 bottles of B mixed together

Volume of Acid in new mixture = 12 + 3 × 10 = 42
Volume of water in new mixture = 18 + 3 × 20 = 78
Ratio of Acid and water in new mixture = 42 : 78 = 7 : 13