How many grams of a 75% acid solution should be added to 30 g of a 15% solution of the same acid to get a 50% solution?

Let’s denote by x – the amount of 75% solution that needs to be added, then the amount of acid will be 0.75x.

30 g of a 15% solution contains 0.15 * 30 = 4.5 g of acid.

We use the formula C = m substance / m solution, we get:

(0.75x + 4.5) / (30 + x) = 0.5;

Let’s solve the resulting equation using the property of proportion:

0.75x + 4.5 = (30 + x) * 0.5;

0.75x + 4.5 = 15 + 0.5x;

0.75x – 0.5x = 15 – 4.5;

0.25x = 10.5;

x = 42 (d).

Answer: You need to add 42 g of a 75% acid solution.