Group data into classes and get frequencies, relative frequencies, and a histogram.
Inputs
Results
5 classes of width 18
The 20 values run from 33 to 120. The tallest class is 51 – 68.
Frequency distribution
Class
Frequency
Midpoint
Relative frequency
Cumulative frequency
33 – 50
6
41.5
0.3
6
51 – 68
7
59.5
0.35
13
69 – 86
4
77.5
0.2
17
87 – 104
1
95.5
0.05
18
105 – 122
2
113.5
0.1
20
On the TI-84
Enter the data in L1. 2nd Y= (STAT PLOT) → Plot1 → On, Type: histogram, Xlist: L1. In WINDOW set Xmin = first lower limit, Xscl = class width. GRAPH, then TRACE.
Xmin=33 Xscl=18
Show steps
Range. max − min = 120 − 33 = 87.
Class width. range ÷ number of classes = 87 ÷ 5 = 17.4. Round up so every value fits: width = 18.
Lower limits. Start at 33 and add 18 each time: 33, 51, 69, 87, 105.
Tally how many values fall in each class. Relative frequency = frequency ÷ 20.
About this calculator
Building a frequency distribution
A frequency distribution groups data into equal-width classes and counts how many values land in each. Pick a number of classes (5 to 15 is typical), find the class width by dividing the range by the number of classes, and always round the width up so the largest value still fits.
Reading the histogram
Each bar's height is a class frequency. Look at the overall shape: symmetric (mirror-image sides), skewed right (long tail toward larger values), or skewed left (long tail toward smaller values). Check for gaps and for any values far from the rest.
Different class widths can make the same data look a little different. That's normal; try a couple of choices.