Father A is twice the age of the difference in years of the ages of Father B and Son A, who is one and a half times older than Son B.

Father B is currently twice the age of Son A is going to be when Son B will be double the age he is now.

All of the ages are multiples of five.

How old is Father A?

(In reply to re: Most realistic solution by Lewis)

The usual understanding would be that Father A, Father B, Son A and Son B are humans; and, with the longevity of a human in recent times being no greater than 129 years, we can, contemporary, logically dismiss the additional solutions leaving the single expected one.  
Yet, these aging individuals could be (1) Giant Tortoises who can have a long life span; or (2) they could be ante-deluvian humans, with an accepted understanding that the biblical ages given of our ante-deluvian kin as accurate, e.g. Methuselah lived 969 years; or, (3) simply humans of the current or near future taking into account recent advancements to extending life expectancy, and thus may live beyond 129 years.  In such cases, the problem does need the additional information, such as 'they all had to be below 100', as indicated in the post, in order to limit the number of solutions to one.

Posted by Dej Mar on 2008-03-28 09:58:57