 Okay, let's go ahead and look at this second problem. This second problem is essentially a density problem. What we're doing is comparing physical properties here. So if the physical property of density is essentially equivalent to the known physical property of a particular piece of wood, in this case oak if it's around 0.9 grams per cubic centimeter and pine if it's around 0.4 grams per cubic centimeter, then you can identify what piece of wood you have. So essentially this is converting from one density unit to another because remember density is mass divided by volume and what we're looking for is grams per cubic centimeter of course which is mass divided by volume but pounds is mass and gallons is volume so you have a mass to volume ratio there. So we're just trying to convert that mass to volume ratio to another mass to volume ratio. And in order to convert anything as you know by now you need a set of conversion factors which I put up at the top of the page there. So you can see there's five of them that you actually need for this problem and you just go ahead and convert each one of them successively. So what I converted first was the mass units from pounds to kilograms and then from kilograms to grams and I stopped there because of course that's the units that I wanted I wanted grams per cubic centimeter and then right now I'm in grams per gallon so that's not what we want the volume unit at least so let's go ahead and convert gallons to liters so using that next conversion factor over that cancels out gallons we still have liters so we're going to convert that to milliliters and then of course lastly we're going to use the last conversion factor to cancel out our mills and get cubic centimeters. Now I'm putting that to 0.88 grams per cubic centimeter the answer to two significant digits because the volume is in two significant digits the given volume and remember you always want to go to the number of sig figs of the given numbers and we see that when we compare our density that we found that we've calculated to the known densities it compares very nicely to the density of oak so we can essentially say that we have a piece of oak here okay so hopefully that makes sense let me know if you have any issues.