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An unknown number is an odd number greater than $$50$$ but less than $$100$$. The number is a multiple of $$3$$ and $$7$$. What is the value of the unknown number? 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples->Common Factors and Common Multiples
A multiple of $$3$$ and $$7$$ also a multiple of $$21$$  $$21\times3=63$$  $$21\times4=even$$  $$21\times5=105$$, exceed  Thus, only $$63$$ 