Eddy is solving the following Math question.     A factory needs to make $$100$$ spare parts. The factory has already made $20$ spare parts in the past $$2$$ hours. Assuming the same speed, how many more hours will the factory need to finish the remaining amount of spare parts?     Below is Eddy\textquotesingle s working:  In $1$ hour $$\rightarrow20\div 2=10$$ spare parts  Time needed $$\rightarrow100\div 10=10$$ hours     Is Eddy correct? If not, show the correct working and find the answer. 
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