Abby is half as old as her dad and as twice as old as her brother. if her brother is 9 years old how old is her dad?

Let Abby's father's age be x.

Then Abby's age = 1/2 x or her father's age = 2 * Abby's age

Abby's brother's age = 9 years

So, Abby's age = 2*9 = 18 years

∴ her father's age = 2*18 = 36 years

A=D/2

A=2B

B=9

A=2 (9)

A=18

18=D/2

*2 both sides

D=36