# Statistics and Probability Terms | Mathematics

Will it rain today? Will traffic be heavy on the way to work? Will my boss be happy with my performance?

These are all questions of prediction. In a previous TASC Test Assessing Secondary Completion™ blog post on statistics and probability, we stated that **every day you use probability when you make predictions and analyze for the best outcome.**

Remember that:

**Statistics**is the study or practice of collecting and analyzing numerical data.**Probability**is the likelihood of something happening.

Let’s review seven key terms that will help advance your understanding and study of statistics and probability:

- A
**hypothesis**is an educated guess/statement that can be tested.- Example: The more a student studies for the TASC test, the higher score his or her HSE score will be.

**Independent events**, A and B, are independent of each other if the fact that A occurs*does not*affect the probability of B occurring.- Example: Without looking, you choose a red pair of socks from your drawer (
**Event A**). Then you put the red pair of socks back in your drawer. Without looking again, you choose a white pair of socks from your drawer (**Event B**).

- Example: Without looking, you choose a red pair of socks from your drawer (
- The
**Mean**is the average of a set of values. The mean is a calculated value. To find the mean of a set of numbers: Add up all of the numbers, then divide by how many numbers there are.- Example:
*Set of values {2, 4, 6, 8, 10}*- Add up all of the values: 2+4+6+8+10 =
**30**. - Then, divide 30 by 5, since there is a total of 5 values in the set.
- 30/5 = 6.
**6 is the mean of this set of values.**

- Add up all of the values: 2+4+6+8+10 =

- Example:
- The
**Median**is the middle number in a set of values.- Example:
*Set of numbers {3, 13, 23, 33, 43}*- The middle number in this set of values is
**23**.

- The middle number in this set of values is
- Example:
*Set of numbers {19, 25, 31, 38, 46, 53}*- This example has an even amount of values.
- To find the median, take the two middle numbers – 31 and 38 – and add them together. 31+38 =
**69**. - Then, divide 69 by 2. 69/2 =
**34.5 is the median of this set of values**.

- Example:
- A
**sample size**is a portion of a population chosen for a survey or experiment.- For example, say you want to survey what the most popular brand of soda is in America. Surveying the entire population would be too expensive and too time consuming. So you take a sample size which can be a few thousand Americans.
- It’s important sample sizes are strategically chosen so it will be a reliable representation of all American’s and their soda preference.

- The
**Standard Deviation**is a measure that shows how spread out a set of data is. The symbol for Standard Deviation is**σ**(the Greek letter sigma) and is defined as the square root of the sample variance.- The formula for Standard Deviation:

Image via: GeographyFieldWork.com

- The
**Sample****Variance**is a measure of the expected deviation from the mean. The symbol for Sample Variance is**s**.^{2}- The formula for Sample Variance:

Image via: StatisticsHowTo.com

Head on over to MathisFun.com to read more about standard deviation and variance and learn how to solve for each.