In one sentence, describe what the following article is about: The density of a substance is equal to its mass divided by its volume. You can measure the mass on a scale and record the volume of the liquid used. Use the equation "m / v = D" where m is mass in grams or kilograms, v is volume in milliliters or liters, and D is density. For example, if you had a sample that was 8 grams and 9 milliliters, your equation would be: "8.00 g / 9.00 mL = 0.89 g/mL." Weigh an empty container first and record its weight. Next, fill your container with the desired liquid and weigh it again. The mass of your liquid is equal to the second measurement minus the first. For instance, if the filled container weighed 2.00 lbs and the empty container weighed 0.75 lbs, the equation would be: "2.00 - 0.75 = 1.25" and the liquid would weigh 1.25 lbs. Between -10 degrees Celsius and +30 degrees Celsius, the density of water can be rounded to 1.00 (assuming 3 significant figures). If you are using liquids that do not fall in that temperature range, you can measure the mass and the volume of your water and calculate the density. Alternatively, you can often find charts with the density of water at different temperatures. It's important to find the density of water that is the same temperature as the liquid in order to get accurate measurements. Substances expand when they are heated and contract when they are cooled. Since density is a measure of how much mass is in a given volume, the measurement is changed by the expansion and contraction due to temperature. If you want to get accurate specific gravity calculations, it is necessary that the liquid you are measuring and the water that you are using as a comparison are both at the same temperature. The units will cancel out in this equation, leaving you with a unitless quantity. That number is the specific gravity (or relative density) of your liquid. The ratio used will be "Dl / Dwater" where Dl is the density of your liquid and Dwater is the density of your water. For example, if you were to take the density of acetone (0.787 g/mL @ 25 degrees C) and divide it by the density of water (1.00 g/mL @ 25 degrees C), you would get 0.787g/mL/1.00g/mL=0.787{\displaystyle 0.787g/mL/1.00g/mL=0.787}.
Summary: Obtain the density for the liquid in question. Obtain the density of an identical volume of water. Keep your liquids the same temperature. Calculate the ratio of the liquid's density to the density of water.

Cardboard is an excellent building medium for beginners. It's also great if you're on a budget as many of your building materials can be found around your home. However, models built from cardboard won't be as durable or sturdy as models built from other materials. Empty cereal boxes, paper towel tubes, and toilet paper tubes are great cardboard building materials. Adhesives include masking tape, craft glue, and spray adhesive. Other household materials such as tin cans and scrap paper can be used as well. Craft foam, also called foam core, is sold in thick sheets at craft stores. This medium will create sturdy and lightweight structures. However, some beginners have difficulty cutting the foam. If you've never used foam before, buy extra sheets to practice on. To work with foam, you will need: A sharp craft knife for slicing the foam A heated foam wire cutter for cutting large pieces of foam (optional) Tacky glue, a hot glue gun, or a liquid adhesive Wood is the best choice for large, sturdy castles. These castles can last years if they're built properly. However, beginners may find woodworking difficult and expensive. Tools for woodworking include: A circular saw for cutting the wood A hammer A screwdriver Wood glue Nails and screws of various sizes Before designing your castle, consider any factors that will affect your design. For example, consider your space limitations. This includes your workspace and the display space. If your design is too large, you won't have anywhere to put your castle. Other things to consider include: What are the limitations of your building medium? For example, paper castles won't last as long as wooden castles. How big is your budget? Paper castles are cheaper than foam or wooden castles. How much time can you devote to your project? Wooden castles are very sturdy, but they will take weeks to complete.
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One-sentence summary -- Decide whether or not to use cardboard. Consider using craft foam. Choose wood as your building medium. Consider your limitations.

Problem: Article: As noted in the intro, there are hundreds of ways to make a BLT. This variation adds a little west coast flair to the standard BLT by adding some of the key ingredients in a California club sandwich. To start, you'll want to build a BLT as directed above until the point just before you'd normally be finished. In other words, cook some bacon, then spread a little mustard and mayonnaise on your bread, and finally add tomato, lettuce, and your cooked bacon to your sandwich. From here, we'll be adding a few extra touches to make our sandwich unique. For a true west coast classic, you may want to consider using sourdough, San Francisco's signature bread. Peel and cut a ripe Hass avocado into several thick french-fry sized slices. Lay these slices down above your final layer of bacon. The avocado gives the sandwich a creamy, satisfying quality not present in an ordinary BLT. The smooth texture of the avocado contrasts especially well with crunchy toast. Avocados are best when they're ripe. Ripe Hass avocados (the most common variety on the west coast) have dark green-to-black skin and a firm, yet yielding texture. The fruit should feel somewhat weighty and should have no obviously flattened or "smooshed" patches. If you're unsure whether an avocado is ripe, check under the brown stem remnant at the bottom of the avocado. If the skin underneath is bright yellow-green, you've picked a ripe avocado. If it's brown, your avocado may be bruised or overripe. After adding your avocado, you may want to squeeze a thin slice of lemon over your sandwich to produce a few drops of lemon juice. If you do so, be conservative you want just a hint of lemony zest, not a BLT that makes you pucker. If done correctly, the BLT will have a slight tangy flavor which, for some, is absolutely mouthwatering when paired with the meatiness of the bacon and the smoothness of the avocado. Congratulations! Your California BLT is ready to eat. If you desire, you can add another layer of ingredients and an additional piece of bread to create a double-decker. If you're looking for a truly Californian experience, you may want to opt for this California clubs, the state's signature sandwich, are customarily served as double-deckers.
Summary:
Assemble a classic BLT, minus the final piece of bread. Add a few avocado slices. Optionally, add a spritz of lemon juice. Add your final piece of bread.