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What is the smallest number with distinct digits whose digits add up to 45?

  • A.123555789
  • B.123457869
  • C.123456789
  • D.99999

Answer: C

The smallest such number is 123456789.

The digits 0 to 9 add up to 45, so distinct digits summing to 45 must be all ten digits or all of 1 to 9 (leaving out 0, which adds nothing). A nine-digit number is smaller than any ten-digit one, and arranging 1 to 9 in increasing order gives the smallest: 123456789.

123555789 repeats the digit 5, and 99999 repeats 9, so neither has distinct digits. 123457869 uses the right digits but is larger than 123456789, because its sixth digit is 7 instead of 6.

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