Key Vocabulary
Mean / Average — add all values and divide by
how many there are.
(promedio / media)
Median — the middle value when data is in order
from least to greatest.
(mediana)
Mode — the value that appears MOST often in a
data set.
(moda)
Range — the difference between the largest and
smallest values.
(rango)
Data Set — a collection of numbers or
information.
(conjunto de datos)
Outlier — a value that is much higher or lower
than the rest of the data.
(valor atípico)
Step-by-Step
Finding the Mean
-
1 Add ALL the values together.
-
2 Count how many values there are.
-
3 Divide the sum by the count.
Finding the Median
-
1 Put the numbers in ORDER (least
to greatest).
- 2 Find the MIDDLE number.
-
3 If two middle numbers, find
their average.
Example Data Set: {12, 15, 18, 15, 20, 22, 15, 28}
Ordered: 12, 15, 15, 15, 18, 20, 22, 28
Mean: (12 + 15 + 15 + 15 + 18 + 20 + 22 + 28)
÷ 8 = 145 ÷ 8 = 18.125
Median: 8 values → average of 4th and 5th: (15 +
18) ÷ 2 = 16.5
Mode: 15 appears 3 times (most often) →
15
Range: 28 − 12 = 16
Watch Out!
-
You MUST order the data before finding the median!
If you don't, you will pick the wrong middle number.
-
Even number of values: Average the TWO middle
numbers to find the median.
-
A data set can have no mode (if no number repeats)
or more than one mode (if two or more numbers tie
for most frequent).
-
Outliers affect the mean more than the median. One
very large or very small number can pull the mean up or down.
Practice Problems
Use this data set: {12, 15, 18, 15, 20, 22, 15, 28}