The following stem-and-leaf plot represents the test scores for 22 students in a class on their most recent test. Use the data provided to find the quartiles.
Test Scores by Student
Stem Leaves
6 1 6 6 6
7 1 3 4
8 1 1 5 5 7 8 8 9
9 1 3 3 3 7 7 7
Key: 6|1=61
Step 2 of 3 : Find the first quartile.
To find the first quartile (Q1), we need to find the median of the lower half of the data set.
The lower half of the data set includes the test scores 61, 63, 66, 66, 67, 71, 73, 74, 75, 78, 83, and 89.
There are 12 scores in the lower half, so the median is the average of the 6th and 7th scores when the data is ordered from smallest to largest.
Ordering the data set: 61, 63, 66, 66, 67, 71, 73, 74, 75, 78, 83, 89
The 6th and 7th scores are 71 and 73.
Thus, Q1 = (71 + 73) / 2 = 72