Vinegar is denser than water
17) 8.4 / 20 x 100
18) 20 . 0.5150
19) 6,50% because (as you said) the law of definite proportions states that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass
Some bad people will tend to forge dollar bills and make fake bills, giving them to cashiers and asking for it to be split into a different amount of bills so they are given real cash and wont be caught or they will buy things, return them and be given back real money and get away with it. This is obviously a crime because it's fake.
