Qualification > Math
S1 and S2 DOUBTS HERE!!!!
ashwinkandel:
I have one confusion. For the question attached below, if we are said to draw a cumulative frequency curve, then can we use 100,150,200 on the x-axis of the curve or should we use 100.5,150.5,200.5 as we use the value of Upper Class Boundary while drawing C.F curve. I am really confused.
Alpha:
--- Quote from: ashwinkandel on October 18, 2011, 01:50:49 pm ---I have one confusion. For the question attached below, if we are said to draw a cumulative frequency curve, then can we use 100,150,200 on the x-axis of the curve or should we use 100.5,150.5,200.5 as we use the value of Upper Class Boundary while drawing C.F curve. I am really confused.
--- End quote ---
You may use 100, 150, 200 etc. You'd use 100.5, 150.5, 200.5 when there wouldn't be an equal sign there. :)
astarmathsandphysics:
Cant see attachement but use 150 etc anyway
ashwinkandel:
@ astarmathsandphysics you can enlarge the attachment by clicking it. I am still in little confusion. I quote one sentence from my statistics books: "The cumulative frequencies are plotted against the upper class boundaries of the corresponding class." Our class boundary is written in the form x-y where x is inclusive but y is not. However, in the given question 150 200 are inclusive. So, to make it exclusive I add 0.5 and make it 150.5. For this same question mean has also been asked for 4 marks. and it has been done by using 0.5-100.5,100.5-150.5... in the mark scheme.By the way, the full question is from CIE 9709 May June 2011 Paper 61 question no. 6. I also read examiner report. In examiner report the statement was like this: "A mark was awarded for attempting to plot the cumulative frequencies against their respective upper class boundaries"
Alpha:
--- Quote from: ashwinkandel on October 18, 2011, 02:23:12 pm ---@ astarmathsandphysics you can enlarge the attachment by clicking it. I am still in little confusion. I quote one sentence from my statistics books: "The cumulative frequencies are plotted against the upper class boundaries of the corresponding class." Our class boundary is written in the form x-y where x is inclusive but y is not. However, in the given question 150 200 are inclusive. So, to make it exclusive I add 0.5 and make it 150.5. For this same question mean has also been asked for 4 marks. and it has been done by using 0.5-100.5,100.5-150.5... in the mark scheme.By the way, the full question is from CIE 9709 May June 2011 Paper 61 question no. 6. I also read examiner report. In examiner report the statement was like this: "A mark was awarded for attempting to plot the cumulative frequencies against their respective upper class boundaries"
--- End quote ---
I did that paper some time back. And I got the same confusion as yours.
Yeah, now I get what you mean. You're right. Less or equal to 100 means it stops at 100. So, you cannot use 100 as the starting point for the other class. You have to add 0.5. Make it 100.5.
It's actually the difference between a discrete and continuous variable. The cumulative frequency uses a continuous variable, when you convert it to a simple frequency table, it becomes a discrete variable.
Hope you get me. :)
And thanks for asking that question. My confusion is cleared, albeit by myself.:P
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