In what proportions should 6% and 20% iodine solutions be mixed to obtain a 10% solution?

Let x be the mass of the first (6% solution), and y is the mass of the second (20% solution).

6% = 0.06; 20% = 0.2; 10% = 0.1.

Let us express the amount of pure iodine in the first solution: 0.06x.

The amount of pure iodine in the second solution: 0.2u.

The amount of pure iodine in the resulting solution: 0.1 (x + y).

0.06x + 0.2y = 0.1 (x + y).

0.06x + 0.2y = 0.1x + 0.1y.

0.2y – 0.1y = 0.1x – 0.06x.

0.1y = 0.04x.

10y = 4x.

According to the rule of proportion: x / y = 10/4 = 5/2.

That is, the ratio of the first solution to the second is 5 to 1.

Answer: the solutions must be mixed in a 5: 2 ratio.