Question 167751
The number of U.S. teenagers in the age category "15-19-years olds" during any year between 1980 and 1998 can be modeled approximately by 
T=332*|x-11.5| + 17000 
where T is the number of "15-19-years-olds" in thousands and x is the number of years since January 1, 1980 (U.S. Census Bureau, Current Poplulatioin Reports.) Use the model to determine the year in which the number of 15-19-year olds in the U.S. was 18,700,000 (18,700 thousands). 
The book comes up with the answer of 1986 and 1996,
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18,700 = 332*|x-11.5| + 17000 
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332*|x-11.5| = 1700
|x-11.5| = 5.12..
x-11.5 = 5.12 or x-11.5 = -5.12...
x = 16.62 or x = 6.38
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1980 + 6.38 = 1986

1980 + 16.62 = 1996
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Cheers,
Stan H.