Donny Dont was asked what mass in kg a substance must have if its density is 3.00 kg/L and it takes up 12.0 gallons of volume. He correctly rearranged the equation for density, d=m/V, to solve for m: m=V*d, but what he put for his answer was “12.0 gal. * 3.00 kg / Liter = 36”. O n!! Donny Dont didn’t include any units after the number 36, and therefore his answer doesn’t really convey any information! He multiplied 12 * 3 correctly, but neglected to multiply or divide units. What units would his answer of 36 be in? Hint: it is a big jumbled mess of units. Ohhh n! Donny also failed to answer with the correct number of significant figures! How many sig figs SHOULD his answer contain?
To correctly do this problem, we need to get the units of volume to cancel, and to do that, we need to make them consistent, perhaps by converting 12.0 gal. to Liters, and then using that number of Liters for V (Conversion factor: There are 3.78 L per gallon). Finish the problem correctly for Donny, so that kg is the unit of your answer, and so that your answer has the correct number of significant figures!