If Larry will be 50 in 25 years, then Larry is currently 25

With the sum of their ages being 75, then 

You should now be able to find his father’s age, 25 years from now.

OR

Let father's age, in 25 years be F

Then father’s current age is: F - 25

If Larry will be 50 in 25 years’ time, then Larry is now 50 - 25, or 25

With their current ages summing to 75, we get: F - 25 + 25 = 75

F, or  

Answer by ikleyn(52785)   (Show Source): You can put this solution on YOUR website!
 .





            This problem can be solved  MENTALLY,  without using equations.







(1)  The last problem's statement is that "Larry will be 50 years old in 25 years".

      Hence, he is  50-25 = 25 years old now.



(2)  "The sum of the current ages of Larry and his father is 75".

     Hence, Larry's father current age is 75-25 = 50 years.



(3)  Therefore, the ANSWER to the problem's question is 50+25 = 75 years:

     in 25 years, Larry's father will be 75 years old.



(4)  Actually, we just answered the problem's question.

     We only need to check that 

          "in 25 years, Larry's father will be thrice as old as Larry today" is valid.


     But 75 = 3*25 is CORRECT, so this statement is TRUE.




The problem is just solved.





The answer to the problem's question is 75 years.





--------------





    In this problem, two statements are independent and necessary: the first and the third.

    The second statement is EXCESSIVE, UNNECESSARY and is not used in the solution.

    This second statement should be checked at the end for the validity after completing the solution,
    to assure that it is consistent with and does not contradict to other given conditions.




 

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