1. Pg 311 No.2
ESTIMATED RANGE = Higher end of Last Group – Lower end of First Group
ESTIMATED RANGE = 60 – 0 = 60
Also, without looking at the original list of raw data we cannot know which time occurred most often, so we cannot find the MODE but we can find the MODAL GROUP or MODAL CLASS.
The MODAL CLASS is 𝟏𝟎≤𝒕<𝟐𝟎
Using just this chart we cannot tell how many times the journey took exactly 45 mins or if it ever took 45 mins at all. Also we cannot read the shortest or the longest time taken.
This means that we cannot give an accurate RANGE but we can give an ESTIMATED RANGE

2. L.O.To be able to create Frequency Polygons
By the end of the lesson we will be able to:
identify the midpoint of grouped data
plot a frequency polygon
identify the modal class and estimated range
WE WILL NOT BE DRAWING PIE CHARTS, PIE CHARTS DO NOT MAKE SENSE FOR A CONTINUOUS SCALE.

3. How can we always find the midpoint (even when not so obvious) ?
Starter
What is the midpoint between the following numbers?
Green
0 – 10
40 – 50
30 – 40
0 – 100
0 – 50
Red
54 – 56
5 – 9
8 – 14
38 – 52
0 – 5 5 55 45 7 35 11
= 10 / 2 = 5
= 90 / 2 = 45
= 70 / 2 = 35
= 100 / 2 = 50
= 50 / 2 = 25
= 110 / 2 = 55
5 + 9 = 14 / 2 = 7
= 22 / 2 = 11
= 45
0 + 5 = 5/2 = 2.5 50 45 25
2.5
How can we always find the midpoint (even when not so obvious) ?

4. Frequency Polygons
An easier and better way of comparing different sets of data is to use a frequency polygon
A frequency polygon shows the trend of the data
You plot the midpoint against the frequency

5. You have drawn your first FREQUENCY POLYGON…YAYY YOU!
Frequency Polygons 10 9 8 7 6
Frequency 5 4 3 2 1
Frequency table can be drawn from a histogram or without histogram by adding a column mid-class value to the Frequency Table
Grab a bright colour and mark the mid-points on the bars of your homework histogram - join
You have drawn your first FREQUENCY POLYGON…YAYY YOU!

6. Example: The weight of 100 dogs at a dogs’ home are shown in the table below.
Frequency 4 13 25 32 17 9
Midpoints
Weight
0 < w ≤ 5
5 < w ≤ 10
10 < w ≤ 15
15 < w ≤ 20
20 < w ≤ 25
25 < w ≤ 30
Frequency 4 13 25 32 17 9
Midpoints
2.5
7.5
12.5
17.5
22.5
27.5
Weight
0 < w ≤ 5
5 < w ≤ 10
10 < w ≤ 15
15 < w ≤ 20
20 < w ≤ 25
25 < w ≤ 30
Frequency 4 13 25 32 17 9 35 30 25
Frequency 20 15 10 5 5 10 15 20 25 30
Weight

7. Add a mid-class value column
Classwork: A survey
Ages of people surveyed  6 of the people surveyed were between 0 and 10 (including 10)
Add a mid-class value column

8. What is the Estimated Range?
What is the Modal Class?

10. What are the steps?
Add a mid-class value column and fill up with the midpoints of the class (add and divide by 2)
Draw the axes, midpoint against frequency
Plot the midpoints (midpoint, frequency)
Join the points to form the frequency polygon

11. Comparing Frequency Polygons
The age when 100 people from the UK and the USA got married for the first time is shown on the frequency polygon below. Write a sentence to compare the data. 40
Key UK
USA 35 30 25
Number of People 20 15 10 5 15 20 25 30 35 40 45 50
Age of First Marriage

12. STP 8 Pg 317 Exercise 15 f No. 2 25- means 𝟐𝟓≤𝒘<𝟑𝟎
Homework
STP 8 Pg 317 Exercise 15 f No means 𝟐𝟓≤𝒘<𝟑𝟎

13. L.O.To be able to create Frequency Polygons
By the end of the lesson we will be able to:
identify the midpoint of grouped data
plot a frequency polygon
identify the modal class and estimated range

14. What is the estimated range?
What is the modal class?