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A large whiteboard has 2014 "+" signs and 2015 "−" signs written on it. You are allowed to delete two of the symbols and replace them according to the following two rules. If the two deleted symbo...
#1: Initial revision
by
will.octagon.gibson
·
2026-08-02T02:30:17Z (about 2 months ago)
Starting with 2014 "+" signs and 2015 "−" signs, you delete signs until one remains. What’s left?
A large whiteboard has 2014 "+" signs and 2015 "−" signs written on it. You are allowed to delete two of the symbols and replace them according to the following two rules. If the two deleted symbols are the same, then replace them by "+". If the two deleted symbols are different, then replace them by "−". You repeat this until there is only one symbol left. Which symbol is it? Justify your answer. --- Attribution: UK Mathematical Olympiad for Girls 2014