Glen is now twenty-one years old and Jerry is fifteen years old. How many years ago was Glenn's age twice Jerry's age.

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Lets use x to represent the number of years ago when that happened. As a result, Glen was 21-x and Jerry was 15-x years old. Since we know that Glen's age was twice Jerry's age, we would have the equation: 21-x = 2(15-x) 21-x = 30-2x 2x-x = 30-21 x = 9 We can check this result: 9 years ago Glen was 12 years old, while Jerry was 6 years old. 12 is twice 6, so we are done! :D