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Daphne, My technique is similar to RD's "without algebra" method but I would list the possibilities differently. The tens digit can be 1 to 9 so start with 1. If the tens digit is 1 and the sum of the digits is 9 then the units digit is 8, Does 18 satisfy the condition that the ones digit is twice the tens digit? Next try the tens digit being 2 and so on. Harley  


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