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# S1 help (histograms) watch

1. Attachment 548955548957

I really don't understand what to do for part C, this is from the June 2014 R paper (edexcel), would appreciate some help.

Thanks.
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2. (Original post by DeRerumNatura)

I really don't understand what to do for part C, this is from the June 2014 R paper (edexcel), would appreciate some help.

Thanks.
The height is frequency density = frequency / class width (full video tutorial here).

For part C is asking you to use linear interpolation, which you would first do by identifying at which class intervals the mean lies. So firstly, do a cumulative frequency table and use n/2 to find the frequency of the mean. Then figure at which group it belongs to and use this simple method:
lower boundary of class + class width x (group frequency - mean frequency / group frequency)
3. (Original post by kkboyk)
The height is frequency density = frequency / class width (full video tutorial here).

For part C is asking you to use linear interpolation, which you would first do by identifying at which class intervals the mean lies. So firstly, do a cumulative frequency table and use n/2 to find the frequency of the mean. Then figure at which group it belongs to and use this simple method:
lower boundary of class + class width x (group frequency - mean frequency / group frequency)
Hi,

Thanks, but how would I do this to get the number of people waiting between 3.5 and 7, which is what the question asks ? And why would you do n/2 I thought that was to find the median ?

Thanks
4. (Original post by kkboyk)
The height is frequency density = frequency / class width (full video tutorial here).

For part C is asking you to use linear interpolation, which you would first do by identifying at which class intervals the mean lies. So firstly, do a cumulative frequency table and use n/2 to find the frequency of the mean. Then figure at which group it belongs to and use this simple method:
lower boundary of class + class width x (group frequency - mean frequency / group frequency)
This is what they do in the mark scheme :

1/3*15 + 9 + 1/2*6 = 17
5. (Original post by DeRerumNatura)
Hi,

Thanks, but how would I do this to get the number of people waiting between 3.5 and 7, which is what the question asks ? And why would you do n/2 I thought that was to find the median ?

Thanks
That was for part d, where you use n/2 for the median.

For C you should use your histogram, since for the previous part you were told to find the height of the group 2-4. Then find the area of the bar from between 3.5 - 4, for 5-6 (which is just 9 from the table) and for 7 (which is just 6 from the the table)

(Original post by DeRerumNatura)
This is what they do in the mark scheme :

1/3*15 + 9 + 1/2*6 = 17
The bit in bold above
6. (Original post by kkboyk)
That was for part d, where you use n/2 for the median.

For C you should use your histogram, since for the previous part you were told to find the height of the group 2-4. Then find the area of the bar from between 3.5 - 4, for 5-6 (which is just 9 from the table) and for 7 (which is just 6 from the the table)

The bit in bold above

Hi,

Thanks so much, I understand it now, I didn't think to use the histogram.

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