AQ3.1: Activity Question 1, Question5-Week 3

[Abhishek Kumar]

As per the lecture Class Mark is the average of lower and upper class limit in a interval.

in the question class interval [55,60) is given

The lower limit is 55 and upper limit is 59. The class mark iwould be 57. However the class mark given in the answer is 57.5.

Kindly correct me if I am wrong.

[Rajesh Saha]

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[Rajesh Saha]

(55+60)/2 = 57.2

[Anand Iyer]

I was confused too, and hence decided to spend some time on this; here's what I found.

As per Neil Weiss's book, there're 3 types of grouping of data.

1.  Single-valued grouping (uses single-value frequencies and graphed with bar charts)

2.  Limit grouping (uses class-intervals - between the lower and upper boundary of each class, and graphed with histograms)

3. Cut-point grouping (uses class-intervals - between the lower boundaries for each successive classes, also graphed with histograms)

The first one is typically used for discrete data.  The third is used to represent continuous data, and the second in both cases.

In our case, we're talking about the 3rd case, since ours is continuous data.

That's the reason, it uses cut-point grouping and hence the limits are different - starts from the lower boundary of the first interval, and ends with the lower boundary of the second interval.

I hope all that makes sense...

Please feel free to challenge me on this:)  I'm no expert.

[Abhishek Kumar]

I don't think the question referred to 3rd case. In my opinion the marks are discrete, but have too many distinct value, thus limit grouping has been used. The upper limit is still 59, the class mark should be 57.

[Anand Iyer]

just for an argument.  

if the questions were anything like those in our own assignments, you might end up with fractional values.

So, the marks could well be treated as continuous.  They're definitely not integers.

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Cheers,

Anand

[Abhishek Kumar]

That make sense....

[Malabika Guha Mustafi]

Anand, yes  it is continuous class interval ( the upper limit of one class is the lower limit of the following class.) . Thank you .  

[Malabika Guha Mustafi]

http://math.fau.edu/~pbudhath/DAY%202_Spring2014.pdf