Solving equations in primary school mathematics: Lao Zhang is 27 years older than Xiao Ming, and Lao Zhang is 4 times older than Xiao Ming. How old is Xiaoming?
Suppose: Xiaoming is x years old. Solution: X=(X+27)/4 multiply both sides by 4:4X = X+27.
3X=27 X=9 (years old) A: Xiaoming is 9 years old.