The answer is: " 100 " .
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Step-by-step explanation:
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Let "x" represent the numerical value of [the man's age].
 500 - 3x = 200 ; Solve for "x" ; 
 Subtract "500" from each side of the equation:
 500 - 3x - 500 = 200 - 500 ; 
to get:
 - 3x = -300 ; 
Now, divide each side of the equation by "-3" ; to isolate "x" on one side of the equation; & to solve for "x" ; 
 - 3x / -3 = -300 / -3 ; 
  x = 100 . 
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The answer is: " 100 " .
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