A twenty percent solution contains 24.3 g of iodine. What is the mass of the entire solution?

According to the condition of the task, a 20% solution is given, which means that every 100 grams of solution contains 20 grams of iodine. Thus, you can make up the proportion:

100 g contains 20 g of iodine,

a in x g – 24.3 g of iodine

and it turns out that

100/20 = x / 24.3.

The product of the extreme terms of the proportion is equal to the product of its middle terms, which means

20 x = 100 * 24.3.

So, x = 100 * 24.3 / 20 = 5 * 24.3 = 121.5 (g).

Answer: the mass of a 20% iodine solution is 121.5 grams if 24.3 grams of iodine are dissolved in it.