SOLUTION: A father is 6 times as old as his son.4 year's later his father will be only 4 times of his son.what are their ages

F = 6*S,             (1)    ("A father is 6 times as old as his son")
F + 4 = 4*(S+4).     (2)    ("4 year's later his father will be only 4 times of his son")


From (1), substitute F = 6*S into equation (2). You will get

6S + 4 = 4S + 16,

2S = 16-4 = 12  ---->  S =  = 6.


Thus, the son is 6 years old now.


Then the father is 6*6 = 36 years old.