Problem 9 · 2023 Math Kangaroo
Medium
Algebra & Patterns
substitutionsum-constraint
The two markers with a question mark have the same number. Which number do you have to put instead of the question mark so that the calculation is correct?
Show answer
Answer: C — 3
Show hints
Hint 1 of 3
Both question marks hide the very same number, so whatever you try, use it in both spots.
Still stuck? Show hint 2 →
Hint 2 of 3
You can just try the answers: put 1 in both marks, then 2, then 3, and check the sum each time.
Still stuck? Show hint 3 →
Hint 3 of 3
Keep trying numbers until the calculation comes out right.
Show solution
Approach: try the same number in both marks until the sum works
- Remember both marks are the same number, so pick a number and use it in both spots.
- Try the choices in turn and add up: too small a number makes the total too low, too big makes it too high.
- The number that makes the calculation come out exactly right is 3, so the answer is C.
Mark:
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