1. The older brother noticed that in 10 years, the younger brother will be as old as he is now, and his age will be twice the current age of the younger brother. How old is the younger brother now?
Answer: 20 years.

Solution. Let the current age of the younger brother be $x$ years, and the older brother be $y$ years. In 10 years, the younger brother's age will be $y$ years, and the older brother's age will be $2x$ years. Since the age of each has changed by 10 years, we have the equations: $y+10=2x, x+10=y$. By adding and simplifying the equations, we get $x=20$.

Criteria. Any correct solution: 7 points.

Correct answer: 1 point.