JAMB - Mathematics (1982 - No. 4)
Seven years ago, the age of a father was three times that of his son, but in six years time the age of the son will be half that of his father, representing the present ages of the father and son by x and y, respectively, the two equations relating x and y are
3y - x = 0; 2y - x = 0
3y - x = 14; x - 2y = 6
3y - x =7; x - 2y = 6
3y - x = 14; y - 2x = 6
x + 3y = 7; x = 2y = 12
Vysvetlenie
7 years ago, Father(x - 7) years old, Son (y - 7) years
x - 7 = 3(y - 7)
x - 7 = 3y - 21
3y - x = -7 + 21 = 14
3y - x = 14 ... (1)
In six years time,
x + 6 = 2(y + 6)
x + 6 = 2y + 12
2y + 12 = x + 6
12 - 6 = x - 2y
6 = x - 2y ... (2)