Lesson 3 Formulas

Question 1

Constructing FDT Step 1:

Range

Answer 1

refers to the difference between the highest and the lowest scores

R = Highest Score – Lowest Score

Question 2

Constructing FDT Step 2:

Class interval (i)

Answer 2

dividing the range by the desired number of class intervals

(i) = Range ÷ Desired Number of Classes

Note: a. when the data are whole numbers, i should also be a whole number
b. When the data are in one-decimal place, i should also be in one decimal place

Question 3

Constructing FDT Step 3:

What is the last step?

Answer 3

Tally the frequencies for each, until the highest value is reached.

Question 4

Class Boundaries (cb)

Answer 4

Lower limit - 0.5
Upper limit + 0.5

Question 5

Class mark (x)

Answer 5

• is the midpoint or middle value of a class interval or class limit
• obtained by finding the average of the lower class limit and the upper limit

x = Lower limit + Upper limit / 2

Question 6

Class size

Answer 6

refers to the difference between the upper class boundary and the lower class boundary of a class interval.

Class size of the class limit 5 – 9 is  4.5 – 9.5 = 5 

Question 7

Relative Frequency (rf)

Answer 7

is obtained by dividing the class frequency by the total frequency

class frequency / total frequency

The class limit 5 – 9 has 6/60 or 0.10 for its relative frequency.

Question 8

Cumulative Frequency (cf)

Answer 8

The less than cf (< cf) can be obtained by adding the individual ferquencies successively starting from the top.

The greater than cf (>cf) can be obtained by adding the individual ferquencies successively starting from the bottom.