Question 174684
 I started working at 15. I spent 1/4 of my working life in a factory. I spent 1/5 of my working life in an office, and I spent 1/3 of my working life as a school caretaker. For the last 13 years of my working life I've been Santa Claus. How old am I?" 
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1/4 + 1/5 + 1/3 = 15/60 + 12/60 + 20/60 = 47/60 of his working life.
The remaining 13/60 must be the 13 yrs as Santa, so that's 60 years.
Add the 15 when he started, and he's 75.
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As a check:
1/4 of 60 = 15
1/5 of 60 = 12
1/2 of 60 = 30
That adds to 47 years.  Add 15 and 13, that's 75.