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2010 Math Kangaroo

Problem 11

Problem 11 · 2010 Math Kangaroo Medium
Arithmetic & Operations order-of-operations

Which of the following expressions has a value that differs from the others?

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Answer: E — \((20 \div 10) \times 20 + 10\)
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Hint 1 of 2
You do not have to finish all five — notice that four of them are built from the same big pieces (200 and 200, or 2 and 200).
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Hint 2 of 2
The odd one out is the one where the last step is adding a small 10, not multiplying.
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Approach: spot the matching values
  1. A and D are \(200 + 200 = 400\); B and C are \(2 \times 200 = 400\) — four of them equal 400.
  2. E is \((20 \div 10) \times 20 + 10 = 2 \times 20 + 10 = 50\).
  3. Only E is different, so the answer is E.
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