Let the cup capacity be 1.

The sugar content after the first pouring is 0.3× (1-0.2)+0.05× 0.2 = 0.25.

After the second pouring, the sugar content was 0.25× (1-0.2)+0.05× 0.2 = 0.21= 21%.

Cultivate interest in mathematics;

Mathematics is the easiest subject for children to get a sense of accomplishment. Through their own continuous thinking, they overcame a difficult problem, got the final answer in different ways, and solved the same problem faster than their classmates, which gave the children a great sense of accomplishment. Especially the classmates, teachers and parents all praised: you are so smart! The child will never be bad at math.