The KSW computer science aptitude test was given to 50 students.
The following frequency distribution resulted from their scores:
KSW Test Scores 0-4 4-8 8-12 12-16 16-20 20-24 24-28
Frequency 4 8 8 20 6 3 1
The data value 12 belongs to which class?
What is the class width?
The highest value possible is 28
The lowest value possible is 0
Subtract 28 - 0 = 28
Divide by 7
Get 4
Round up to the next higher whole number, which is 5
So the class width is 5
Start by subtracting .5 from the least possible value,
0 - .5 = -.5
Starting with -.5
add 5 to that, get 4.5
add 5 to that, get 9.5
add 5 to that, get 14.5
add 5 to that, get 19.5
add 5 to that, get 24.4
add 5 to that, get 29.5
So there are only 6 classes because
we did not need a 7th class since 28
is the largest possible score.
The 6 classes are:
-0.5 -- 4.5
4.5 -- 9.5
9.5 -- 14.5
14.5 -- 19.5
19.5 -- 24.5
24.5 -- 29.5
This way, no score lies on the boundary between
any two classes, because the scores are all whole
numbers, and the boundaries between the classes are
not whole numbers.
We can now easily see that 12 belongs to the class
9.5 -- 14.5
Edwin