Question 174684
8-year-old Samantha visited Santa at a local department store. He gave her this riddle: 
" 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?" 
The problem says you need to explain how you got the answer and how you know it is correct. 
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Let "x" be the number of working-life years.
factory time: (1/4)x
office time : (1/5)x
school time : (1/3)x
Santa time  : 13 years
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Working-life equation: (1/4)x + (1/5)x + (1/3)x + 13 = x
15x + 12x + 20x + 60*13 = 60x
47x + 60*13 = 60x
13x = 60*13
x = 60 (years he worked)
Age = 15 + 60 = 75 yrs. old
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Cheers,
Stan H.