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Romanian District Olympiad 2015, Grade VI, Problem 1

Source:

September 25, 2018
arithmeticromania

Problem Statement

On a blackboard there are written the numbers 11 11 and 13. 13. One step means to sum two written numbers and write it. Show that:
a) after any number of steps, the number 86 86 will not be written. b) after some number of steps, the number 2015 2015 may be written.
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