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My sentence is:

"Visit us December 10th, 11th, 12th and enjoy twice the savings!"

Should their be one more and? (Like this:)

"Visit us December 10th, 11th, and 12th and enjoy twice the savings!"
Or do you have any better suggestions?
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It's a pretty simple concept as an advertisement, so I don't think you need to worry overmuch; but if I were punctuating, I would write:

"Visit us December 10th, 11th and 12th-- and enjoy twice the savings!"

or

"Visit us December 10th through 12th-- and enjoy twice the savings!"
Comments  
'Visit us December 10th through 12th and DOUBLE your savings!'