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Perfect Ruler

Problem

By marking off six unit lengths on a piece of wood, we can make a ruler to measure all the lengths from 1 to 6 units directly.


But it is possible to achieve the same thing by using just two marks.


What is the minimum number of marks necessary to measure all the lengths from 1 to 12 units?

Problem ID: 70 (Mar 2002)     Difficulty: 2 Star

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