Problem in S1( Maths P6)

[Shujaat Khan]

Uhm so yeah regarding cumulative frequency,
1. Can we draw a cumulative frequency polygon instead of a curve if it says draw cumulative frequency graph?
by polygon i mean joining points plotted with ruler.

2. Anyone can tell me when do we need to use boundaries instead of real values for x-axis?
I see multiple different questions and I'm always confused
e.g x<20....
-20,-30....
20-,30-.....
10-20,21-30..... AND 10-20, 20-30...
And for the =< stuff there are too many I just need the logic behind. An example is 10<x=<20

 

[DarkEclipse]

1. No.

2. When they tell you to draw a histogram, and then find the mean/variance/standard deviation.

 

[Shujaat Khan]

1. No.

2. When they tell you to draw a histogram, and then find the mean/variance/standard deviation.

Sorry but histograms and cumulative frequency are 2 different graphs?!
Besides many questions asking mean/sd use and dont use boundary for each kind

 

[bakhita]

Since you know that cumulative frequency polygon and a curve are both different, and the values (if asked for in the question) to be configured from the graph, might result different. Another reason why you can't use polygon instead of a curve is that the mark scheme shows it as a curve. Here is a question from Oct/Nov 2014:
It asks for a frequency graph exactly as you mentioned and here is it's mark scheme:

It shows a curve and not a polygon. In fact, to be on the safe side, we must do what the mark scheme shows us.
The same explains your other question as well. As you can see, the given Heights have gaps between their range. For example, it says 4-10 then 11-15, if they are plotted as it is, the values between 10-11 do not exist since our values ended at 10 and started from 11. Therefore, we have to create a bridge between them, which is done by adding the last value of the previous range with the first value of the next range and then dividing them by 2. In this case: 10 + 11 = 21, 21/2 = 10.5.
However, if the question had ranges like 4-10 and 10-15, there was no problem in plotting them without their class boundaries.

 

[DarkEclipse]

Sorry but histograms and cumulative frequency are 2 different graphs?!
Besides many questions asking mean/sd use and dont use boundary for each kind

I meant that use boundaries whenever they ask for histograms, and when they tell you to derive the mean from the histogram data.

 

[Shujaat Khan]

Thanks to both of you, cleared some doubts in my head. Will try my best to aim for that A* in maths