Deriving and changing the subject of formulae
 

Deriving and changing the subject of formulae problem 30


John was to celebrate his birthday. In the invitation he told his friends how old he will turn in a riddle.


"Today, my father is three times as old as I am". When I celebrate my birthday on Friday, I will be a year older, and my father will still be the same age. At that time, we will be 53 years old altogether."


What birthday will John be celebrating?


 

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