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The digits of a two-digit number add up to 9. When the digits are reversed, the new number is 27 more than the original. What is the original number?

Competition practiceNumber System, HCF & LCM
  • A63
  • B36
  • C45
  • D27

Step-by-Step Solution

Let tens digit a, units b: a + b = 9 and 9(b − a) = 27, so b − a = 3. Then a = 3, b = 6, giving 36 (63 − 36 = 27).
Answer: B) 36

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