The age difference between elder brother and younger brother is three times.
3 1- 1 = 30 years old
My brother is older than my brother.
30 ÷ 3 = 10 years old
This year's brother
3 1- 10 = 2 1 year
This year's brother
21-10 =11year
Or a series of equations. ...
Solution: Suppose my brother is now X years old and my eldest brother is Y years older than my brother. So my brother's age now is X+Y. It can be listed as follows:
X+y+y=3 1① x+y is the age when the younger brother grows up to the age when the older brother is now, plus y is the age when the older brother is 3 1 year old.
X-y= 1② The age of a brother in his younger brother is X, minus Y is the age of his younger brother at that time, that is, 1.
X=y+ 1③ comes from ②.
Substitute ③ into ① to get.
y+ 1+y+y=3 1
The answer is y= 10.
x = y+ 1 = 1 1； x+y = 1 1+ 10 = 2 1。