The task is to generate the correct answer for a given math problem.

[Q]: Problem: a father said to his son , ` ` i was as old as you are at the present at the time of your birth ' ' . if the father ' s age is 52 years now , the son ' s age 5 years back was :
[A]: d ) 21


[Q]: Problem: if each participant of a chess tournament plays exactly one game with each of the remaining participants , then 153 games will be played during the tournament . find the number of participants .
[A]: 18


[Q]: Problem: the sum of the numbers is 550 . if the first number be twice the second and third number be one - third of the first , then the second number is :
[A]:
150