Amouthwash is 38.1% ethanol by mass. if each bottle contains 1.040 pints of mouthwash with a density of 0.851 g/ml, how many kilograms of ethanol are in 160 bottles of the mouthwash

Total mass of mouthwash = volume*density
1 pint is 568.261 mL therefore 1.040 pints = 591.0 mL (4 significant figures)
Therefore mouthwash mass in a bottle = 591.0 mL * 0.851 g/mL = 503 g (3 s.f.)
In 160 bottles, ethanol mass = 509 g * 160 * 0.381 = 30700 g = 30.7 kg

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It shows that the experiment is designed properly.