Final answer:
Seven years ago, Jack was three times older than his sister.
Explanation:
Jack is 16 and his sister is 10. Let x be the number of years ago when Jack was three times older than his sister.
Equation based on the given information: 16 - x = 3(10 - x)
Solving the equation: 16 - x = 30 - 3x ==> 2x = 14 ==> x = 7 years ago.
Therefore, 7 years ago, Jack was three times older than his sister.
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