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.
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