How many 16.9 ounce bottles of water will equal to a half gallon?

1 gallon = 128 fluid ounces

1/2 gallon = 128/2 = 64 ounces

Number of bottles = 64/16.9 = 3.787

In order to get 1/2 gallon, you have to open 4 bottles,
but you have 0.213 bottle or 3.6 ounces left over.