Summary: Finding Averages and Basic Probabilities

Key Concepts

• Calculate the mean of a set of numbers.
  1. Write the formula for the mean $\text{mean}=\frac{\text{sum of values in data set}}{n}$
  2. Find the sum of all the values in the set. Write the sum in the numerator.
  3. Count the number, n, of values in the set. Write this number in the denominator.
  4. Simplify the fraction.
  5. Check to see that the mean is reasonable. It should be greater than the least number and less than the greatest number in the set.
• Find the median of a set of numbers.
  1. List the numbers from least to greatest.
  2. Count how many numbers are in the set. Call this $n$ .
  3. Is $n$ odd or even?If $n$ is an odd number, the median is the middle value.If $n$ is an even number, the median is the mean of the two middle values
• Identify the mode of a set of numbers.
  1. List the data values in numerical order.
  2. Count the number of times each value appears.
  3. The mode is the value with the highest frequency.

Glossary

mean

The mean of a set of $n$ numbers is the arithmetic average of the numbers. The formula is $\text{mean}=\frac{\text{sum of values in data set}}{n}$

median

The median of a set of data values is the middle value.

• Half the data values are less than or equal to the median.
• Half the data values are greater than or equal to the median.

mode

The mode of a set of numbers is the number with the highest frequency.

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