400 g of 20% sugar syrup was diluted with 100 g of water. What is the concentration of the resulting syrup.

20% is one fifth of 100%. 20% of any weight is also a fifth of this weight, or this weight should be multiplied by 0.2. Let’s calculate the amount of sugar in the original syrup in grams:
400/5 = 400 * 0.2 = 80;
After adding 100 g of water, the syrup began to weigh 500 g, but there was still 80 g of sugar in it. What percentage is this?
80/500 = 8/50 = 16/100 = 0.16.
The syrup is now 16%.
Answer: The concentration of the resulting syrup is 16%.