Correlation refers to the statistical relationship between two quantities. The correlation coefficient is a single number that you can calculate for any two sets of data points. The number will always be something between -1 and +1, and it indicates how closely connected the two data sets tend to be. For example, if you were to measure the heights and ages of children up to the age of about 12, you would expect to find a strong positive correlation. As children get older, they tend to get taller. An example of negative correlation would be data comparing a person's time spent practicing golf shots and that person's golf score. As the practice increases, the score should decrease. Finally, you would expect very little correlation, either positive or negative, between a person's shoe size, for example, and SAT scores. The arithmetic mean, or "average," of a set of data is calculated by adding all of the values of the data together, then dividing by the number of values in the set. When you find the correlation coefficient for your data, you will need to calculate the mean of each set of data. The mean of a variable is denoted by the variable with a horizontal line above it. This is often referred to as "x-bar" or "y-bar" for the x and y data sets. Alternatively, the mean may be signified by the lower-case Greek letter mu, . To indicate the mean of x-data points, for example, you could write x or (x). As an example, if you have a set of x-data points (1,2,5,6,9,10), then the mean of this data is calculated as follows: x=(1+2+5+6+9+10)/6{\displaystyle \mu _{x}=(1+2+5+6+9+10)/6} x=33/6{\displaystyle \mu _{x}=33/6} x=5.5{\displaystyle \mu _{x}=5.5} In statistics, standard deviation measures variation, showing how numbers are spread out in relationship to the mean. A group of numbers with a low standard deviation are fairly tightly collected. A group of numbers with a high standard deviation are widely scattered. Symbolically, standard deviation is expressed with either the lower-case letter s or the lower-case Greek letter sigma, . Thus, the standard deviation of the x-data is written as either sx or x. The summation operator is one of the most common operators in mathematics, indicating a sum of values. It is represented by the upper-case Greek letter, sigma, or . As an example, if you have a set of x-data points (1,2,5,6,9,10), then x means: 1+2+5+6+9+10 = 33.
++++++++++
One-sentence summary -- Understand the concept of correlation. Know how to find a mean. Note the importance of standard deviation. Recognize summation notation.

Q: Even if you've washed, exfoliated, and moisturized your face, your pores may still look large. Applying a silicone-based foundation primer can fill in your pores, so they aren't as noticeable and you have a smooth canvas to apply your foundation over. Apply your primer with clean fingers so you can be sure to really work it into your pores. Opt for an oil-free, mattifying primer to keep your pores looking small all day. Check the label on your primer to make sure it is designed to minimize pores. Any makeup that has a dewy or luminous finish calls attention to the texture of your skin, including large pores. Make your pores appear smaller by using a matte foundation that won't reflect light and highlight your pores. Matte foundation also keeps the skin from looking shiny throughout the day, so your pores will stay minimized. Opt for a matte foundation that's oil-free and non-comedogenic so your pores stay as clear as possible. Brushing or smoothing foundation over enlarged pores usually causes the makeup to catch in them and emphasize their size. Instead, press and buff the foundation into your skin in circular motions. Pressing fills in the pores, while buffing helps cover them for a minimized appearance. A full, dense foundation brush is ideal for pressing and buffing your makeup in. However, you can also use an egg-shaped sponge to apply your foundation in a similar manner. Wet the sponge and wring it out before using it, though, so it doesn't absorb too much of your makeup.
A: Use a silicone-based foundation primer. Choose a matte foundation. Press and buff the foundation into your skin.

Article: Pick up the knife from your place setting with your dominant hand. Hold it with the index finger along the top part of the handle. In a standard place setting, the knife will be placed on the right side. This is because most people are right-handed. Pick up the fork from the table using your non-dominant hand. Hold it with the points facing downward towards your food and your index finger on the back of the handle. For example, if you are right-handed, then pick the fork up with your left hand. Flip it so the pointy parts, called the tines, are facing the table and place the tip of your index finger on the back of the handle around the part where the handle is curved. . Place the tines of the fork against the food you want to cut and slice off a piece with the knife. Only cut a bite at a time and eat it before you cut the next piece. You should never place your cutlery down on the table after cutting your food and starting to eat. Cutting up all your food at once and then placing your knife down is also considered an etiquette no-no. In some cases, it is acceptable to eat using only a fork. For example, when you are eating just a salad or a bowl of spaghetti, it is not necessary to use a knife. Keep your knife in your dominant hand the whole time you are eating. It is, of course, acceptable to use your fork to scoop certain types of foods that naturally can't be speared. You can use the knife to help push food that can't be speared, like rice, onto your fork. This is the only time it is considered polite to place your fork and knife down during dining. Place all cutlery meant for that course, even if you didn't use a particular utensil, onto the plate when you are finished. For example, if the main course was spaghetti and you only used a fork to eat it, you should still place the knife on the plate when you are finished eating. Make sure to place the fork tines-down to indicate that you are finished. For example, this is especially important if you are in a European restaurant and you want the waiter to see that you are done.
Question: What is a summary of what this article is about?
Hold the knife in your dominant hand. Hold the fork points-down with your non-dominant hand. Cut a bite of your food with the knife while using the fork to stabilize it. Use the tips of the fork to spear your food and bring it to your mouth. Put your cutlery on the plate side-by-side, angled to the right, after you finish.