The sum of the ages of Mr. Tan and his son David is 61 years. The difference in their ages is 29. How old is David? How old will Mr. Tan be when David is 21 years old.
Tan will be 50 years old. If the difference in ages is 29, then it will ALWAYS be that, presumably. Therefore, when David is 21, his father must be 29 + 21 = 50. So, so SIMPLE!!
