Respuesta :
Let y= years ago when dad's age was 4 times son's age
60-y=4(30-y)
60-y=120-4y
-y+4y=120-60
3y=60
y=60/3
y= 20 years ago
Then 30-20= 10 yrs. old, the boys age when his dad was 40 years old.
60-y=4(30-y)
60-y=120-4y
-y+4y=120-60
3y=60
y=60/3
y= 20 years ago
Then 30-20= 10 yrs. old, the boys age when his dad was 40 years old.
Then 30-20= 10 yrs. old, the boys age when his dad was 40 years old