Based on the information given the original size of the bottle is 17.5 ounces.
Using this formula
Original size of the bottle
=New bottle size / Percentage increase
Where:
New bottle size=18.4 ounces
Percentage increase=(1+0.05)=1.05
Let plug in the formula
Original size of the bottle=18.4/(1+0.05)
Original size of the bottle=18.4/1.05
Original size of the bottle=17.5 ounces
Inconclusion the original size of the bottle is 17.5 ounces.
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