Problem 11 · 2010 Math Kangaroo
Medium
Arithmetic & Operations
off-by-one
Matthias and Klara live in a tower block. Klara lives 12 floors above Matthias. One day Matthias climbs the stairs to visit Klara. When he is halfway there he is on the 8th floor. On which floor does Klara live?
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Answer: B — 14th
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Hint 1 of 2
Halfway up the climb, Matthias has gone up half of the 12 floors.
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Hint 2 of 2
Find Matthias's floor first, then add 12 for Klara.
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Approach: use the halfway floor to find the start
- Half of the 12-floor climb is 6 floors, and that point is the 8th floor.
- So Matthias starts on the 8 − 6 = 2nd floor.
- Klara lives 12 floors higher: 2 + 12 = 14th floor.
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