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Australian AMC 2018 - Upper Primary Question 25

AMC AUSTRALIA · Australian AMC 2018 - Upper Primary

Question 25

What is the sum of the digits in the result of the subtraction

$$\underbrace{111\ldots111}_{20\text{ digits}}-\underbrace{222\ldots222}_{10\text{ digits}}$$

where the first number has 20 digits each 1, and the second has 10 digits, each 2?
  1. 72
  2. 81
  3. 89
  4. 90
  5. 99