Problem 13 · 2022 Math Kangaroo
Stretch
Arithmetic & Operations
sum-constraint
The numbers in the five circles around each house add up to 20. Some numbers are missing. Which number does the question mark stand for?
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Answer: D — 9
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Hint 1 of 2
The two houses share their two middle circles.
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Hint 2 of 2
Work out the shared pair from the left house, then use it on the right house.
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Approach: use the shared circles between houses
- Left house: 6 + 2 + 5 plus the two shared middle circles = 20, so the two shared circles add to 7.
- Right house: 3 + 1 + (the ? circle) + the same shared 7 = 20.
- That leaves the ? circle = 20 - 3 - 1 - 7 = 9.
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