>>...ten years ago, a father's age was three times the age of his son...<< That says- = 3× >>...ten years later,the father's age will be twice the age of his son...<< That says + = 2× Now write the two equations in F and S, use substitution and find their ages. I won't tell you the answers, but I'll tell you that when you get the answers if you add their ages, you'll get 100. Edwin