The digits of a two-digit number add up to 7. When 9 is added to the number, its digits are reversed. What is the number?

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A 34
B 43
C 25
D 52

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Answer: A. 34

Let the number be 10a + b with a + b = 7. Reversing adds 9 when b - a = 1, so a = 3 and b = 4, giving 34. Check: 34 + 9 = 43. For 25, adding 9 gives 34, not 52.

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The digits of a two-digit number add up to 7. When 9 is added to the number, its digits are reversed. What is the number?

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